The purpose of this paper is to evaluate the trajectory of Kiyomi Morioka’s research from a contemporary perspective in relation to postwar Japanese family sociology and family change. Dividing his research trajectory into four stages, he determined the research topics to pursue in each stage by examining and reflecting on his achievements in the previous stage. After the preparatory first stage, he established the nuclear family theory and summarized the family cycle theory in the second stage. However, at this time, Morioka recognized the limitations of the family cycle theory and expected to overcome these limitations in the third stage by means of the life course theory. At the same time, he showed a strong desire to develop his own theory of family change, but he was unable to achieve satisfying results. In the midst of the increasing dissolution of families, such as “individualization,” and the trend toward diversification in family research, he entrusted the challenge of a paradigm shift to subsequent generations.