Objectives: Considering the importance of assessing the range of phenomena that can change in psychodynamic therapy, and lack of appropriate assessment scale in Persian language, the present study assessed the reliability of the Persian mastery scale. The mastery scale is a comprehensive research tool for assessing a patient's mastery of transference-related interpersonal conflicts during the treatment process. Methods: After preparing the Persian version of the mastery scale through the forward-backward translation process, a sample of 36 relationship episodes was rated by three independent judges. Data were collected in Mashhad, Iran in 2015. The psychometric properties of the instrument, including inter-rater reliability and test-retest analysis were assessed. Results: The test-retest correlations of the 3 judges were (0.80, 0.91 and 0.95), highly significant at P < 0.0001 and the inter-rater reliability indicated a good level of agreement (The ICC (3, 3) 0.84, 95% CI [0.72, 0.90]). Conclusions: The current study has provided evidence that the Persian mastery scale is a reliable instrument for assessing changes in inner capacities and resources through psychodynamic treatments. However, further studies are required to investigate the validity of this scale.