This study aimed to determine the effectiveness of schema therapy on cognitive bias and self-criticism in adolescents with social anxiety disorder. The research method was a quasi-experimental study with a pretest-posttest design and a control group. The statistical population consisted of 83 male adolescents with social anxiety disorder who were referred to psychological centers in Ramsar in the first quarter of 2024. A sample of 30 individuals was selected using purposive sampling and randomly assigned to the intervention group (15 individuals) and control group (15 individuals). For data collection, the Social Anxiety Questionnaire (SAQ) by Connor et al (2000), the Cognitive Bias Questionnaire (CBQ) by Wiseman and Beck (1978), Self-Criticism Questionnaire (SCQ) by Thompson and Zarouf (2004) were used, and for intervention, the Schema Therapy (STP) by Young was used. The data were analyzed using multivariate analysis of covariance. The results showed that by controlling for the pretest effect, there was a significant difference between the posttest mean of the experimental and control groups at the P˂0.001 level. According to the research findings, it can be concluded that schema therapy is useful in reducing cognitive bias and self-criticism in adolescent boys with social anxiety disorder.