Introduction: Social anxiety is one of the most common types of anxiety disorders. Numerous factors play role in etiology of the disorder, including anxiety sensitivity and cognitive distortions. The aim of this study then was to investigate the effectiveness of a modular cognitive behavioral therapy on anxiety sensitivity and cognitive distortions in girls with social anxiety. Method: A semi-experimental design with pretestposttest and control group was applied. The statistical population of the study consisted of all female students with social anxiety in Mashhad. The statistical sample consisted of 24 students with social anxiety, who were selected by available sampling method and assigned to the experimental and control groups. The revised Cox and Taylor anxiety sensitivity questionnaire, Beck and Weisman cognitive distortions were used for data collection. After performing the pre-test, the experimental group underwent intervention for 10 sessions of 90 minutes, while the control group was placed on the waiting list. Post-test was also performed immediately after the treatment sessions. Data extracted and analyzed by an ANCOVA statistical analysis. Results: The results of analysis of covariance showed that by controlling the effect of pre-test in the post-test stage, there is a significant difference between the control and experimental groups in the variables of anxiety sensitivity and cognitive distortions. So that the experimental group showed a significant decrease compared to the control group. Also, the results of the study showed a decrease in the subscales of fear of anxiety reactions, fear of cardiovascular and respiratory symptoms and lack of cognitive control of his anxiety sensitivity subscale. Conclusion: According to the research findings, since patients with social anxiety have symptoms of anxiety sensitivity and cognitive distortions, the use of modular cognitive-behavioral intervention as an effective treatment in patients with social anxiety is recommended.