Aims: Leptin is a polypeptide that is correlated with body weight changes and energy consumption and affected by exercise training. The aim of the present study was to determine the effect of 6 weeks resistance training on body composition, serum leptin and muscle strength in non-athletic men. Materials & Methods: In this semi-experimental trial, 22 non-athletes male living in dormitory of Zanjan University, who were enrolled in 2011-12 academic year were selected with purposive sampling method and randomly assigned to experimental (n=12) and control (n=10) groups. The experimental group performed training program based on the protocol of Kramer and Ratns for 6 weeks (3 sessions per week). At the beginning and end of the research, muscle strength, body composition and serum leptin were measured. Serum leptin was measured by ELISA. Independent T and paired T tests were used to analysis the data in SPSS 16 software. Findings: After 6 weeks of strength training, changes in serum leptin levels and body composition (fat mass without fat) between the two groups was not statistically significant (p>0.05). But in experimental group, the upper and lower body strength training was significantly increased compared with pre-test in control group (p<0.05). Conclusion: It seems that no significant changing in serum leptin levels after a period of resistance training is due to no changing in body fat and not enough exercise, but this training cause in increasing muscle strength.