The purpose of this study is to survey social maturity of children and analyze the factors which are supposed to influence the development of social competence of them. A form of questionnaire was devised which contained 180 items refering to social maturity. These items are grouped into those seven aspects as "Occupation", "Locomotion", "Communication", "Socialization", "Spontaneity", "Self-control" and "Fundamental habits" (cleanliness, toilet habits and dressing, sleeping, feeding oneself). The questionnaire was filled out by the mothers and teachers or sometimes fathers of 3000 children of 11 kindergardens, 8 nursery schools and 15 elementary schools which were sampled from every main part of Japan. Ages of the children ranged from 4 years to 8 years. The results of the survey of social maturity and analysis of the factors influencing children's social competence were as follows ; 1. Urban children were superior to rural ones in social competences. 2. There was no significant difference between males and females. 3. Every aspect of social competences seemed to develop as the individual grows. "Spontaneity", "Self-control" and "Fundamental habits" developed relatively sowly with ages ; however, "Fundamental habits" were established by the age of five. 4. Twin, immature and premature children showed slow development in social competence. 5. The development of social competences is closely related to the number of the family members. For example, a child who lived with no others than his father and mopther showed lower SQ than the one who lived with brothers and sisters. It was found that children acquired social competences through physical maturation and learning. An important thing to be investigated in the future is when and how a child best develops his social competences at a given age.