Objective: Acceptance and commitment therapy has been used to treat anxiety disorders recently. The purpose of this study was to investigate the effectiveness of acceptance and commitment therapy for psychological symptoms in students with social anxiety disorder, including difficulty in emotion regulation, psychological flexibility based on experiential avoidance, self-compassion, and external shame. Methods: This study was a semi-experimental clinical trial. Twenty four students with social anxiety disorder were randomly divided into two groups after initial evaluations: an experimental group (12 subjects) and a control group (12 subjects). The experimental group received 12 treatment sessions based on a protocol of acceptance and commitment therapy for anxiety disorders, and the control group was put on a waiting list. Self-Compassion (SCS), Difficulty in Emotion Regulation (DERS), External Shame (ESS), Social Anxiety (SPIN), and Acceptance and Action (AAQ-II) questionnaires were used to assess participants. Data were analyzed using SPSS. Results: Acceptance and commitment therapy was shown to be effective at the post-test and follow up stages for reducing external shame, social anxiety, and difficulty in emotion regulation and its components, and for increasing psychological flexibility and self-compassion (p < 0.05). The largest effect size of treatment was for increase of psychological flexibility and the lowest efficacy was for the components “difficulty in impulse control” and “limited access to emotional strategies” at the post-test and follow-up stages, respectively. Conclusion: Acceptance and commitment therapy may be an appropriate psychological intervention for reducing the symptoms of students with social anxiety disorder and helping them to improve psychological flexibility. Emotion and related problems can be identified as one of the main targets of this treatment. Clinical trial registration: Iranian Registry of Clinical Trials, IRCT20180421039369N1.