The current study sought to clarify the materials provided by Genjiro Oka (1901–84), an official at the Ministry of Education in Japan, during science education reform in postwar Japan. An analysis of documentary records revealed four main findings: (1) G. Oka’s private library contained 727 Japanese books and 72 foreign books. The foreign books included writings by K.M. Harkness, V.T. Edmiston and H. Heffernan. These books are thought to have been given to G. Oka by three officials at the CIE. (2) Comparing the “Course of Study in Elementary Science” (1947) compiled by the Ministry of Education with “Science in General Education” (1938) by K.M. Harkness revealed that the former writing quoted a section on evaluation from the latter writing. In addition, “Science in General Education” (1938) appears to have influenced “Objectives of Understandings” (1947) compiled by the Advisory Committee on Science Curriculum in Japan. (3) Comparing “Course of Study in Elementary Science” (1947) with “Course of Study in Elementary Science, Spokane Public Schools” (1943) written by V.T. Edmiston revealed that the educational contents from the 1st grade to the 3rd grade in the former writing were quoted from the basic science concepts of the latter writing. (4) It appears that G. Oka made use of the foreign books provided by the officials at the CIE when he compiled “Course of Study in Elementary Science” (1947) and “Objectives of Understandings” (1947).