& aim: Post-traumatic stress disorder can reduce the quality of life and increase in the risk of suicide and psychiatric disorders, as well. Few studies have been done to investigate the effectiveness of metacognitive model for treatment of these patients. This study aimed to investigate the effectiveness of metacognitive therapy on metacognitive beliefs in patients with post-traumatic stress disorder. Methods: This is a single-case study conducted using the multiple baseline design. The

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... ion of the study included all patients with post-traumatic stress disorder in the city of Tabriz in 2015 .The subjects consist of three patients with post-traumatic stress disorder were referred to psychiatrist and selected based on purposive and convenience sampling methods. Patients were evaluated in pre-treatment, during treatment and follow-up period of six weeks using the standard scales. Percent of improvement and effect size were used to analyze data. Results: The results of the study showed that metacognitive therapy significantly reduced metacognitive beliefs and post-traumatic stress disorder in the both post-treatment and follow-up stages statistically and clinically. Percent of improvement for the first, second and third participants was 54.74, 51.09 and 50.65, respectively. Conclusion: The results showed that the clinical effectiveness of metacognitive therapy was confirmed in a culture other than the culture of the manufacturer's treatment protocol so that this treatment is probably effective to reduce the metacognitive beliefs of post-traumatic stress disorder.