The purpose of this study is to examine the relationship between interpersonal competence and classroom cooperation activities. This study selected and evaluated sixteen university students in problem-based learning (PBL) course. The students answered the same questionnaire before and after the cooperative learning of PBL, and the changes in their interpersonal competence were measured. The statistical analysis involved a paired samples t-test. The results suggest that the cooperative learning of PBL develops students' interpersonal competence in a statistically significant way. A qualitative analysis of the students' responses to the questionnaire also reveals the students' changing attitudes toward cooperative learning in the classroom environment.