Introduction: This study aimed to investigate the effect of schema therapy in reducing aggression and social anxiety in adolescents aged 17 to 18 years.

Method: This is a semi-experimental study with multistage cluster sampling method. The population of the study consisted of 3,000 secondary school students in District 1 of Hamadan. In the first stage of sampling, between the two regions of education in the city of Hamadan one was randomly selected. In the next phase, of all secondary schools in the area one was randomly selected and 32 patients were selected from among the students of this school. The Buss-Perry Aggression Scale and the Social Anxiety Scale of adolescents was conducted on students. 16 students were placed in the experimental group and control group and the experimental group received the independent variable (Schema Therapy) for 10 sessions. Each session was 60 minute long.

Findings: The results showed that schema therapy was an effective way to reduce physical aggression (P=0/05, F=20/3), verbal aggression (P=0/05, F=16/6), anger (P=0/05, F=104/5), hostility (P=0/05, F=7/2) and social anxiety (P=0/05, F=8/9) in adolescents aged 17 to 18 years in Hamadan city.

Conclusion: result show the significant effect schema therapy on aggression and social anxiety in adolescents aged 17 to 18 years.