This study focused on (1) the effect of peer counselors´ training on peer counselors´ helping skill and self-concept, and (2) the effect of peer group counseling on senior high school students´ interpersonal problems. In the first part, thirty three female senior high students were selected andserved as proposed peer counselors. These students participated in a eightweek peer counselors´ training program which stressed on knowledge of the peer counselor´s role, understanding of self, and basic interpersonal and counseling skills. The trainees completed the Empathy Scale and Tennessee Self Concept Scale (TSCS) at the beginning and the end of the training session. After the training, six peer counselors were selected and intensively trained as leaders of three T-Groups of tenth female graders with interpersonal problems. Twenty six students who didn´t take the training served as the control group. The second part of the study was the three T-Groups led by six peer counselors (n=20 in total). The control group (n=20) did not participate in any T-Group. The measurement used in this study included: Empathy Scale, TSCS, MPCL, FIRO-B, and Sociometrics. A 2×2 analysis of variance (ANOVA) with repeated measure, Timm´s general linear model and t-test were used to test the hypotheses. Following are the main conclusions: 1. For the peer counselor-there were significant differences between experimental and control groups on empathy skill and self-concept. 2. For the client-there were no significant differences between experimental and control groups on interpersonal problems and interpersonal orientation. However, there were significant differences in pre-and post measures on emotional expansiveness and the selecting index. Results indicated that the training program had a singificant effect on the empathy skill and self-concept of the students. The T-Groups led by the peer counselors were helpful in enhancing the emotional expansiveness on their interpersonal adjustment and the innterpersonal needs. Future recommendations for further research included the training of peer counselors, and the source of the T-Group members.