A study was conducted to assess the social skills of junior high school students in physical education classes, and to investigate how students use their skills, based on a comparison of sex, grade, and differences in adjustment to physical education classes. First, 41 social skill items were collected from previous studies, and then factor analysis was conducted on data from 797 junior high school students. As a result, four factors related to social skills in physical education classes were identified: "maintaining norms skills", "expressing skills", "empathizing skills", and "asking-for-distributing skills". The reliability was confirmed using Cronbach's α. Furthermore, the content validity and the construct validity were verified as satisfactory. Next, the usage of the four social skills by the students in physical education classes was considered, and it was found that: (1) Male students tended to use assertive skills predominantly, whereas female students tended to use maintaining friendship skills. (2) Upper grade students showed a tendency not to use social skills as much as lower grade students. (3) Students who adjusted to physical education classes had a better grasp of social skills during the classes than students showing maladjustment.