The objective of this experimental study is to investigate the effectiveness of smalla dn big group guidance on the self-concept of the adolescence, using cognitive behaviour therapy and multidimentional self-concept model. The effectiveness of this interventions is measured by looking at the improvement of self concept and the evaluation of self concept by peer group, resiliency and decrease of aggressiveness in the experiment group. This research was carried out among the form four student of two secondary schools in Selangor. The measurement used in this study are questionnaire about personal information, Multi dimentional self concept scale. resiliency scale and aggressiveness scale. A total of 104 subject were selected for this research and they were divided into two groups: controlled and experimental group. The subject in experimental group are given about eight sessions of group guidance within eight weeks. The data were analysed using descriptive analysis, ANOVA, MANCOVA and post hoc test. The result showed that the treatment used in the intervention were effective in improving the self concept and the evaluation of the self concept. The finding implies that the small and big group guidance using cognitive behaviour therapy and multi dimentional self concept model has an effect on the self concept of the student.