This paper focuses on Social Capital defined by researches and research institutions. Based on these definitions, Social Capital researches are classified from the perspective that component researchers focus to define. Three components of Social Capital include trust, network, and reciprocity. Following the above, future problems about Social Capital research are discussed. The remaining major problems are summarized by the following two points. First, the implementation of research that has both a theoretical and empirical point of view. Second, the consideration of Social Capital measuring index and analytical method for empirical analyses. Social Capital research in Japan is later developed in comparison with foreign research. Further accumulated research about Social Capital will be required.