The purpose of this study was to examine the effect of the encouragement group counseling on the aggression and peer relationship of discouraged elementary school students to find out the ways of lowering the occurrence of aggression and improving peer relationship. For this study, after administrating the self-discouragement inventory (24 questions) among 54 students of 6th graders from B elementary school in A metropolitan city, top 30%(16 students)of the students were randomly assigned to experimental and control group. After group counseling, the aggression scale (30 questions) and peer relationship scale (20 questions) were administered to find out how encouragement group counseling had an effect on the aggression and peer relationship. To verify the effect of the encouragement group counseling, pre and post-test data were analyzed through the SPSS 24.0. The results of this study were as follows. First, encouragement group counseling had a positive effect on lowering the aggression of the discouraged elementary school students. Also, there was significant difference on the hostility, a sub-factor of the aggression. Second, encouragement group counseling had a positive effect on improving the peer relationship of discouraged elementary school students. Also, there were significant differences on the presence and reliability of friends, the adaption between friends, the co-living with friends. According to the results of the study, counseling implications, limitations of the study, and suggestions for future research were proposed.