Purpose: The purpose of this study was to determine the mediating role of self-differentiation in the relationship between personality traits and perfectionism in students. Methodology: The present study was descriptive in terms of purpose, and in terms of data collection, it was a descriptive correlational design and a path analysis method. The statistical population of the study was all students of Azad University of Science and Research Branch in the academic year 2018-19. The sample consisted of 300 students who were selected by cluster random sampling. Research instruments included Perfectionism Scale Frost (1993), Differentiation Scale Skowron and Friedlander (1998) and Five-Factor Personality Questionnaire Costa and McCreary (1985). Data analysis was done by path analysis and Sobel test at the significant level of 0.05. Findings: The results of data analysis showed that despite the indirect effect of agreeableness, openness to experience and conscientiousness on perfectionism was confirmed by differentiation. On the one hand, differentiation was influenced by personality traits on the one hand and had a significant effect on perfectionism on the other hand (P <0.005). Conclusion: Given that high perfectionism plays a significant part in the development and persistence of individual problems, it can be acknowledged that personality traits influence perfectionism by considering the mediating role of differentiation.
