Introduction: Physical activity and exercise play a role in reducing body image dissatisfaction and body mass index. The aim of this study is to determine the effect of aerobic exercises on body image concern, identity crisis and BMI modification, in girls with body image concern.

Methods: The study is a quasi-experimental with pre and post -test. The study population included all high school girls in Tabriz whom were selected by convenience sampling and filed "Body Image Concern Inventory". 52 of the students with high scores on body image dissatisfaction is selected. Then the “Personal Data Questionnaire” and “Ahmadi Personal Identity Questionnaire”, of which the construct validity and reliability have been reported in pervious study is used in collecting data. The sample students participated in the aerobic exercise for twelve sessions. Finally the post-test is completed and Data are analyzed with SPSS.23.

Results: There is a significant difference between pre-test and post-test variables; dissatisfaction with body image, identity crisis and BMI (P < 0.01). In addition, there are negative and significant correlation between dissatisfaction with body image (r = -0.3, P < 0.03) and identity crisis (r = -0.3, P < 0.02) with BMI modification (P = -0.02, P = 0.03). Finally, the BMI modification index decreased 0.3 units per unit of the dissatisfaction of body image and identity crisis.

Conclusions: Participation aerobic exercises can reduce BMI, concern of body image and crisis of identity in students. Therefore, to enhance the body image dissatisfaction, crisis of identity and body mass index, it is suggested to encourage and increase the participation of adolescents in sport activities.