Abstract Introduction: This study was conducted to find the effect of instructing role-play on improving self-concept of adolescent girls. Methods: At first, all students in one of the mid-schools in Tehran were selected by census and filled out Beck self-concept inventory. In the second step, 202 students who got the lowest scores were selected and randomly divided into two groups (101 in case and 101 in control group). Then, the case group had six 90-minute sessions of instructing role-play. At the end of the training, both groups had a test. Data were analyzed using mean score difference analysis of pre-test, post-test and t test. Results: The results showed a significant difference between the students who received the training and those who did not with regards to self-concept. Conclusion: Instructing role-play can be used as an efficient way to improve self-concept in adolescent girls.