Aim. The aim of this study was to compare BMI and the effects of a session of acute exercise on serum beta-endorphin levels among the sprint swimmers and runners. Methods. In a semi-experimental study, 15 healthy skilled male swimmers (mean and SD of age: 21.64 +/- 2.35, weight: 75.25 +/- 9.81 kg, height: 180.31 +/- 4.75 cm), and 14 healthy skilled runners (age: 21.38 +/- 2.76, weight: 69.78 +/- 6.86 kg, height: 182.21 +/- 5.22 cm), purposefully and voluntarily participated in this study. Venous blood samples of the subjects were taken in three stages 1) basic conditions; 2) immediately after each field of specialized training, with an intensity equal to 8085 % VO2max 30 minutes after exercise in the fasting state. Data was analyzed using with repeated measures (ANOVA). Results. The body composition and anthropometric variables assessed in the study were not significantly different between the 2 groups, except BMI, which was significant (P<0.05). The baseline beta-endorphin serum levels were significantly higher in swimmers than runners (P=0.009). There were significant differences between levels of beta-endorphin of male sprint runners and swimmers in the three periods before, immediately after and 30 minutes after exercise (P <= 0.05). Conclusion. The results showed that Increased fat storage may underlie the higher BMI observed in swimmers compared to runners and B-Endorphin Serum Levels was in swimmers more than runners and an acute exercise session significantly increases the levels of beta-endorphin serum hormone in sprint swimmers and runners.