The purpose of this study is to clarify the differences of social skills development due to the camper's characteristics such as their sex, grades, past camp experience and the differences of social skills that they acquired before the camp. Furthermore, the validity of the Pre-Post model that make the first day of a camp the starting point to measure social skills development is examined. The measurement of social skills was conducted to the 36 campers (32 analysis candidates) at the two weeks before, the first day, the 10th, the final day of the camp and one month after the camp by using social skills measure developed by Shoji (1994). The campers were composed of elementary school (grade 5 and 6) and junior high school children.<BR>Main findings were as follows; 1) Positive and assertive skills influences modification process of social skills. 2) The junior high school student, campers who have past camp experience and camper who had low social skills score showed distinguished increase between before and after the camp. 3) The score of social skills of the elementary school children and the campers who didn't have a past camp experience showed distinguished decrease from two weeks before the camp to the first day of the camp. 4) It is possible that increase social skills from the first day of the camp are recovery process of decrease social skills. From these results, it became clear that the differences of social skills development due to the camper's characteristics in a long period of camp.