Our aim was to investigate the role of serum leptin levels in the control of fat mass in Professional athletes. 7 female and 7 male athletes were included in this study. Test subjects have been active in sports life for 2 years. First blood samples were taken at the period when athletes prior began exercise after a 2 month break. The second and third sampling time were at the end of 2nd month and 4th month of exercise period. When we examined the blood samples taken 3 times in a 4 months period with intervals of 2 months, we did not determine a significant change in serum glucose and leptin levels in pre-exercise and post-exercise periods, whereas serum insulin levels after exercise period were found significantly lower than pre-exercise period. When males and females were compared separately with their own groups, in males and females of control group, serum low density lipoprotein (LDL-C) ( p<0.01; p<0.01 respectively) and leptin (p<0.01; p<0.05 respectively) levels before exercise period were found significantly higher than the post-exercise period in 4 th mounth, whereas high density lipoprotein (HDL-C) levels were found significantly lower (p<0.01; p<0.001 respectively).As a result we observed that medium level exercise exceeding has a suppressor effect on serum leptin levels connected with reduction of body fat ratio.