The purposes of this study are to clarify the effect of participation in the sport club upon personality development and to gain some basic data to be used for the guidance in the sport club, especially in the community sport clubs which are remarkably increasing recently. The subjects used in this study were a total of 254 children (149 boys and 105 girls) who participated in Kyoto City Mini-Basketball Club and were examined from 1975 to 1978, and 500 of non-member school children (245 boys and 255 girls) examined in 1978. All of them were between 10 and 12 years of age. Sociometric Test and Yatabe-Guilford Personality Inventory were conducted together with the examination of behavioral characteristics and sports skill and the following results were obtained: 1) After discussing inclusively their out-door playtime and the number of friends outside of the club, it is presumed that those who are the members of the mini-basketball club have more emotional stability and leadership. Furthermore, girls show more social adjustment and tend to be more active than non-member school children. 2) The children in the mini-basketball club tend to organize sub-groups according to the primary schools they belong to, and in the case of boys, they are apt to gather around a popular person who is an "old-timer" in the club. 3) Generally speaking, the children Who hold higher rank in Sociometric Status mark greater scores in emotional stability, activity and leadership in Y-G Personality Inventory (show type D), and also in sport skill test. Furthermore, they show brightness, cheerfulness, promptness, kindness and attractiveness in terms of their behavioral characteristics.