In 1941 Japan attacked the USA at Pearl Harbor causing the USA to enter World War II on the side of China. China was now allied with the USA, Britain and the Soviet Union in fighting international fascism. In fact, "volunteer" aviators from the USA known as the "Flying Tigers" fought alongside the Chinese. For the first time ever, China had a very positive image among the US public. The Chinese were hailed as heroes fighting against the common enemy, Japan's fascism and imperialism. More than anyone else, it was China's first lady who charmed the public opinion of the USA. China was ruled by Chiang Kai-shek (known as Jiang Jieshi in Mandarin China) and in February 1943 he sent his US-educated wife, known simply as Madame Chiang, on a "goodwill" tour of the USA. She became the second woman and the first Chinese to ever address the US Congress (a nationally-broadcast speech). She was received enthusiastically in San Francisco in March. Following her visit, and the dramatic change in the perception of Chinese people that she generated, the Exclusion Act was finally repealed in December of the same year.

However, the same "Magnuson Act" that in 1943 ended 62 years of Chinese "exclusion" also established a yearly quota of only 105 visas for Chinese immigrants: it didn't exactly open the gates to Chinese immigration. The story was different for Japanese Americans (many of them third generation), who were interned in concentration camps like Manzanar by the tens of thousands. Ironically, this reversed the situation of the previous 40 years, when the Japanese had been able to acquire farmland from expelled or disillusioned Chinese farmers: in 1942 many farms run by ethnic Japanese were taken over by Chinese farmers.

Until the 1940s China was de facto a "western" country. Chinese scientists such as Ta-You Wu (who graduated from the University of Michigan in 1933) shared research with US and European scientists. Chinese universities were world-class universities. The scions of wealthy families often studied at western universities, like the female physicist Chien-Shiung Wu, who graduated from the University of Michigan in 1936, went to work with Emilio Segre' at UC Berkeley and later worked on the atomic-bomb project for the USA (the "Manhattan Project"). Wen Tsing Chow arrived in 1941 to study at MIT and in 1956 invented the programmable read-only memory (PROM), originally for a military project (an airborne digital computer for an intercontinental ballistic missile). Jeffrey Chuan Chu arrived in 1940 and ended up at the University of Pennsylvania's Moore School, working as an electronic engineer on the pioneering electronic computer ENIAC in the team led by John Mauchly and Presper Eckert. Chung-chin Kao studied in Europe but in 1942 moved to the USA working for the Chinese military during the war but based in New York. After the war he joined IBM where in 1947 he built the first electric typewriter for the Chinese language, whose 36 keys were able to produce thousands of Chinese characters, a machine that also pioneered "predictive typing" (based on most frequently used phrases and characters).

Other Chinese moved to the USA thanks to US scholarships. Yung Wing, educated at a Christian missionary school in Canton/Guangzhou, was sponsored by a missionary to study at Yale University and in 1854 became the first Chinese student to graduate from a US university. Upon returning to China, he convinced the Chinese government to establish the Chinese Educational Mission in 1872, which every year for four years sent 30 Chinese teenagers to study Western culture in the USA (in Connecticut). After the failed Boxer insurrection of 1899-1900, the foreign powers forced China to pay indemnity for the damages caused to their Chinese possessions. In 1909 the US government, under pressure from missionaries, decided to return some of that money in the form of a scholarship program for Chinese students to be educated in the USA: the Boxer Indemnity Scholarship Program. To prepare the students, in 1911 the USA funded the establishment of Tsinghua College (today's Tsinghua University). The students were selected through a very competitive process: between 1909 and 1937 (when World War II started), the scholarship sent about 1,300 Chinese students to study in the USA out of the tens of thousands who applied. Most of the "winners" went to MIT. This scholarship became a model for the future Fulbright Program. Among the students who arrived thanks to the Boxer Indemnity Scholarship Program were Hsue-shen Tsien (Xuesen Qian), one of the founders of the Jet Propulsion Laboratory (JPL) in 1936 at CalTech (accused of being a communist and expelled by the USA in 1955, he would launch the space program of Mao's China); and the winners of the 1957 Nobel Prize in physics: Chen-Ning Yang and Tsung-Dao Lee, two Chinese who had studied with Enrico Fermi at the University of Chicago in the 1940s. Tsou Tang arrived in 1941 and graduated from the University of Chicago in 1951, later becoming an influential political scientist. One of the Chinese students who arrived in 1943 and went to MIT was Ju-Chin Chu (Rujin Zhu), father of future Nobel laureate Steven Chu. Before and during the war, China also had a program to train young engineers abroad for two years. One of the last ones to benefit from that program was An Wang, a graduate from Chiao Tung/ Jiao Tong University in Shanghai (the "MIT of China") who arrived in the summer of 1945 and was accepted at Harvard. Wang later founded Wang Laboratories, the company that in the 1970s revolutionized word processing and killed the typewriter.

Another wave of educated Chinese immigrants started in 1949, when Mao's communists seized power in China. One of the scientists who fled China in 1949 was Shu-tian Li, maternal grandfather of the same future Nobel laureate Steven Chu: he had graduated from the USA in 1926 but had returned to China to found several colleges and universities in western and southwestern China. And so the 1997 Nobel Prize in Physics, Steven Chu, was born and raised in the USA, but was the son of a Chinese immigrant of the 1943 wave and grandson of a Chinese immigrant of the 1949 wave.

When his father (a physicist who had graduated in the USA in the 1920s) died in 1949, Chih-Tang "Tom" Sah was adopted by William Everitt, a dean of Engineering at the University of Illinois, and went on to graduate from Stanford University, to join Shockley's lab in 1956 and then Fairchild in 1959, where in 1963 he and Frank Wanlass invented CMOS logic, a fundamental step in the development of computers. Sah literally witnessed the birth of Silicon Valley.

An important event for the many Chinatowns was a ruling in 1948 by the Supreme Court that de facto banned limitations on what a Chinese could own. The Chinese population of the USA had been deprived for three decades of the right to buy a home outside their Chinatown by the various Alien Land Laws. Now they were finally able to move into other neighborhoods of their city. Within a few decades, the Chinese that moved out of Chinatown changed the demographics of San Francisco's Richmond and Sunset districts, and wealthy Chinese families began moving to the suburbs of the Bay Area, like Millbrae, Cupertino (founded in 1955) and Fremont (founded in 1956 near the historic Mission San Jose'). The city of Cupertino counted about 500 families, and several Chinese families ran the main industries of Cupertino: flowers and orchards. Finally, in 1952 the "white person" restriction of the Naturalization Act of 1790 was abolished (with the "McCarran–Walter Act") so that now non-white immigrants could become citizens just like white (i.e. European) immigrants.

In 1949 Mao Zedong's communists won the civil war and seized power in mainland China, establishing one of the most isolated regimes in the world, while Chiang Kai-shek's government fled to Taiwan, which became de facto an independent country. For mainland Chinese, it wasn't just difficult to enter the USA: it was even difficult to leave China. Right after the 1949 revolution the USA received thousands of political refugees who were escaping Mao's regime. The few Chinese students who visited the USA in the 1950s were strongly encouraged to become US citizens and stay because the USA was now afraid of leaking know-how to the communists. For example, Chung-mou "Morris" Chang (the future founder of TSMC) moved to the USA via Hong Kong after his family fled the mainland in 1949 and then studied at Harvard, MIT and Stanford universities, and joined Texas Instruments in 1958.

The annual immigrant quota for China was 105 but between 1953 and 1956 the Refugee Relief Act added about 200,000 special non-quota immigrant visas for refugees and escapees from communist countries, and Chinese refugees received 2,000 of these visas. Ethnic Chinese in the USA increased to 150,000 in 1950 and 237,000 in 1960. But soon immigration from mainland China became virtually non-existent for three decades. The Chinese of America knew little of what was happening in China during the dramatic years of the Great Proletarian Cultural Revolution, launched by Mao in 1966. It was literally another world: the USA was experiencing an economic boom while people in China were starving. All sorts of Chinese businessmen in San Francisco and Los Angeles were becoming rich, while their relatives in mainland China lived in utter destitution.

Respectability came also because of the success of ethnic Chinese politicians: in 1950 Gary Locke, a third-generation Chinese American, became governor of Washington State, the first Chinese-American governor of the USA; and in 1959 Hiram Fong (the son of a Cantonese who had immigrated to Hawaii in 1872) became the first Chinese-American senator.

It is telling that in 1952 the television series "The Gallery of Madame Liu-Tsong" became the first television program with a Chinese-American lead (the already famous Anna May Wong).