According to the Body Mass Index, overweight and obesity in adolescents has increased. Review of clinical trials to determine the effect on adolescents’ Body mass index with twelve weeks of exercise compared to a control group. PUBMED, WOS, SCOPUS, BEIC, JSTOR, and SCIELO data sources. Inclusion criteria: 1. Adolescent population; 2. Body mass index results; 3. Clinical trials; 4. groups with exercise and control; 5. Spanish, English, and Portuguese language; 6. Publications up to February 2021; Keywords: Adolescents, Body Mass Index, Exercise and Clinical Trial. Data extraction: effect on the Body mass index and its standard deviation. 8 studies (N: 761). Exercise significantly reduced the Body mass index of adolescents - 0.57 Kg/m² (-0.7 to -0.5) p < 0.01. Statistical heterogeneity (I²: 89%). 12 weeks of exercise are effective at decreasing Body mass index in adolescents.