Recent critical studies of the history of physical anthropology view Sejin Rha’s (1908-1984) research on Korean populations (hanminjok) after World War II as a continuation of prewar Japanese colonial science. Taking into account the so-called revolution of physical anthropology in the United States in the 1950s, these studies have maintained that Rha’s research program only repeated traditional Japanese colonial anthropology without engaging the new revolutionary development in the field. This article challenges current understandings of Rha’s studies of Korean populations, chiefly his article in 1964, by considering his peripheral position between two metropolitan sciences: prewar Japanese colonial science and postwar US international science. By tracing the changing scientific contexts during the 1930s-1960s to which Rha belonged, this article argues that Rha produced a hybrid physical anthropology program. In particular, he sought to identify Korean populations as those of a biologically unitary nation (danil minjok). To do this, he selectively amalgamated theories, methodologies, and data from both the traditional Japanese colonial anthropology and the seemingly new US physical anthropology into his research program. This case study offers a critical examination of physical anthropology as a way to consider the so-called scientific dimensions of Korean scientists such as Rha who received Japanese colonial education. By situating a Korean scientist between two intellectual traditions, this article contributes to scholarship of the history of science in postcolonial Korea.