The word pseudoscience, what Michael Gordin called “a term of abuse,” had wide valence in twentieth-century China. Having been previously used to mean “empty philosophy,” pseudoscience was attached to Mendelian-Morganist genetics when Lysenko’s doctrine dominated Chinese academic biology in the early 1950s. In the 1980s, however, the term switched to contain research practice perceived as factually suspicious and often politically powerful. Instead of tracing the changing interpretations of pseudoscience confined within one national context, this talk shows a transnational dimension of these changes. Especially, it compares two Chinese-American biologists, Ching Chun Li (C. C. Li, 1912 – 2003)’s and Man-Chiang Niu (1912 – 2007)’s experiences in forming US-China ties, doing biology in China, being criticized as practicing pseudoscience, and their subsequent defense. It shows the ruptured notion of pseudoscience in China is probably best understood as consequence of and circumstance for a continuing transnational dialogue about the relation between science and politics. In particular, population geneticist Li had worked under the Communist rule in the late 1940s when Lysenkoist doctrine was being promoted. He eventually fled to the United States and devoted much energy in criticizing methodological unsound science in eugenics and intelligence testing while becoming a tenor in the chorus of denouncing Lysenko. Developmental biologist Niu, however, started to work with Chinese scientists in the 1970s during the early years of reopening of Sino-American scientific exchange. His projects on cytoplasmic inheritance that used mRNA to generate novel traits in goldfish and to transfer soybean protein to rice became heavily criticized in both countries in the 1980s. Critics occasionally referred Niu as a “Chinese Lysenko.” The disproportionately magnified criticism of Niu carried the momentum of the US scientists’ caution against sloppy methods and the Chinese scientists’ post-Mao skepticism of high political visibility. The path of US-China split and eventual convergence regarding what could be seen as pseudoscience not only challenges the prevalent historiography of science in twentieth-century China, but also shows the pivotal role of traveling scientists during the economic reform in reinterpreting contemporary Chinese history.