Introduction: Necdin is an important negative regulator of white adipogenesis. The acute effect of aerobic exercise on necdin concentration is unclear; therefore the present study was conducted to determine the effects of a bout of intensive aerobic exercise on necdin concentration in obese and lean men. Material & Methods: Eighteen sedentary obese (Age: 21.7 ± 2.1 and BMI: 33.7 ± 2.1 kg/m2; ± SD, n = 9) and lean (Age: 20.5 ± 0.7 and BMI: 17.6 ± 1.6 kg/m2; ± SD, n = 9) men volunteered to participate in this study. All the subjects were performed the Bruce test as the intensive aerobic exercise. Blood samples were taken before and immediately after the intensive aerobic exercise. Results: No significant differences were observed at baseline in necdin concentration between obese and lean subjects (35.8 ± 24.2 vs. 21.9 ± 16.2 pg/ml; P = 0.2 respectively). After an intensive aerobic exercise necdin concentration increased significantly in the lean subjects (21.9 ± 16.2 to 65.9 ± 86.1 pg/ml; P = 0.01) however no significant changes were observed in the obese subjects (35.8 ± 24.2 to 36.9 ± 19.3 pg/ml; P = 0.5). The results revealed that necdin concentration was higher in the lean subjects in compare to the obese subjects (P = 0.03) in response to a bout of intensive aerobic exercise. Conclusion: The results of present study suggest that necdin concentration increases in response to acute aerobic exercise in lean subjects. Future studies are needed to examine the effect of exercise training on necdin levels in the obese subjects. Manuscript profile