This study identifies the role of the Social Studies Unit Plan in experimental schools designated by the Textbook Bureau of the Ministry of Education, by analyzing the process of introducing "Unit of work" at the Elementary School Attached to Tokyo Second Normal School. To fulfill the above-mentioned purpose, this study was conducted by focusing on the modification process of the Social Studies Unit Plan, which was carried out from May to November 1947 at the School. First, the modification process of Social Studies Unit Plan was examined and the process whereby "Unit of work" was introduced and the reasons for this were clarified. Next, there was a clarification of the outcome of the social studies curriculum research of the Seminar in Elementary Education which impacted on the modification process. Having done this, the facts regarding the process whereby "Unit of work" was introduced into Social Studies Unit Plan were clarified. Finally, reference was given regarding the role fulfilled by Social Studies Unit Plan in Experimental Schools designated by the Textbook Bureau. The above examinations revealed the following. Firstly, the introduction of "Unit of work" was carried out in order to modify the Social Studies Unit Plan (introduced in May 1947) which was created without properly understanding "Unit of work" and without considering the actual conditions in the local community. Therefore, the understanding of social studies of America was deepened through the research related to social studies and free study, and through participation in the Seminar in Elementary Education. Second, a "community survey form" and "How to develop a Unit of work" were created at the Seminar in Elementary Education. Third, the school modified the Social Studies Unit Plan according to the "community survey form" and "How to develop a Unit of work." Consequently, the modified Social Studies Unit Plan (introduced in November 1947) comprised units for the studying of local community, and the relation of this to free study, the "unit of work" already taught and the "Problem Unit" of the Course of Study for the Social Studies I (Tentative,1947) was emphasized. "How to develop a Unit of work" was affected by part of the development of the Seminar in Elementary Education's "How to develop a Unit of work." Finally, I emphasize that the school made use of the acceptance of the "community survey form" and "How to develop a Unit of work" in Seminar in Elementary Education through a research approach that valued the relationship between social studies and free study. Therefore, the "Unit of work" was introduced as a Social Studies Unit Plan in the School. As seen in the trends in the School, experimental schools helped in creating the Social Studies Unit Plan, which introduced "Unit of work" before the issue of The Supplement to the Course of Study for the Social Studies in Elementary Schools (1948), through the crystallization of the Course of Study for the Social Studies I (Tentative,1947), as well as in adopting and implementing a process of trial and error on the theory of social studies of America.