Introduction: Obesity is a complex disorder, which is characterized by excessive accumulation of adipose tissue. Leptin is a peptide hormone, which is basically secreted by adipose tissue and is effective in the regulation of body weight and fat. The purpose of this study was to investigate the effect of high-intensity interval training on the level of Leptin and liver enzymes in obese and overweight males. Materials & Methods: In this semiexperimental study, 22 males with the mean age, height, weight, and body mass index of 12-14 years, 164. 43± 5. 11cm, 74. 02± 12. 34 kg, and 29. 27± 4. 09, respectively, were selected voluntarily and randomly divided into experimental (n=11) and control groups (n=11). The experimental group was subjected to 8 weeks training program (three 40-min sessions each week) which included 10 sets of cycling on a cycle ergometer for 60 seconds with 80 % intensity of the reserve heart rate. Blood samples were taken 24 and 48 hours before and after the training, respectively, in a fasting condition. Leptin, Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), and Alkaline phosphatase (ALP) were measured using specific methods. Body fat percentage, body max index, and maximum volume of oxygen were evaluated before and after the training. ANOVA was utilized to analyze data. Finding: According to the results, there was a decrease in the levels of ALT and body fat percentage as well as an increase in the maximum volume of oxygen in the experimental group, compared to the control group (P<0. 05(. Moreover, the levels of Leptin, AST, and ALT decreased; however, the difference was not statistically significant )P<0. 05(. Ethics code: IR. IAUETB. 1395. 52005 Discussion & Conclusions: High-intensity interval training on a cycle ergometer can be an appropriate exercise strategy to reduce the plasma concentration of ALT and body fat percentage in obese and overweight males. However, the intervention should be longer to achieve desired results.