After entering the bloodstream and crossing the blood-brain barrier, Cathepsin B can improve memory and learning by increasing BDNF expression. The purpose of study was to investigate the effect of an acute bout of resistance exercise on serum levels of Cathepsin B and BDNF in male bodybuilders. In this quasi-experimental study, 21 males (age: 27.95±3.96 years, weight: 79.09±9.35 kg, height: 176.90±4.74 cm) voluntarily participated. Subjects were randomly divided into two control (n=10) and experimental (n=11) groups based on 1 repetition maximum of squat and chest press exercises. Three days before the training, fat percentage and 1RM of squat and bench press exercises were measured. On training day, the subjects of training group (N=11) performed Squat, Leg Extension, Barbell Bench Press, Dumbbell Bench Press, Barbell Shoulder Press, Behind-the-Neck Press, Lateral Pull-Down, Cable Seated Row and Sit-Up, 4 sets/10 reps at 70% 1RM. Blood samples were taken 5 min before and after the training. ELISA kits were used to measure levels of BDNF and Cathepsin B. Data were analyzed using Covariance analysis and Pearson correlation coefficient and the level of significance was considered as p <0.05. The results showed that one session of resistance exercise significantly increased serum levels of BDNF and Cathepsin B (p˂0.05). In addition, there was a nonsignificant positive correlation between lean body mass and baseline and post exercise serum levels of BDNF (r=0.41 and r=0.17 respectively) and Cathepsin B (r=0.17 and r=0.06 respectively) (p˃0.05). Also, there was a positive nearly significant correlation between increases in serum levels of BDNF and Cathepsin B (p=0.065, r=0.574). Moderate-intensity resistance exercise increases serum levels of BDNF and Cathepsin B in male body builders, which probably can be effective in improving memory and learning.