Abstarct: Abstract Introduction: This study aimed to investigate a period of exercise activity with different intensities on decorin gene exxpression through interaction with transforming growth factor-beta (TGF-β) in male adult rats. Materials & Methods: This experimental study included 24 males adult Wistar rats that were divided into three groups (8 animals per group) of High-Intensity Training (HIT), Low-Intensity Trainin) LIT), and Control. Training groups trained for eight weeks and five days week. The HIT group exercise program consisted of one hour of exercise for five 8-min intervals at 85%-90% Vo2max that were separated by 2-min intervals with an intensity of 50%-60% Vo2max. On the other hand, the LIT group exercise program included five 8-min intervals with an intensity of 55%-60% Vo2max, and 2-min intervals with an intensity of 45%-50% Vo2max. It should be noted that the control group received no exercise program. Findings: The results of this study showed that the exxpression levels of the decorin gene in the HIT training group were significantly higher than those in the control group (P=0.001), whereas the levels of decorin in the LIT training groups were not significantly different from those in the control group (P=0.11). The exxpression levels of the TGF-β gene in both training intensities (high- and low-intensity training, respectively) showed a significant difference, compared to the control group (P=0.001, P=0.18). Discussions & Conclusions: According to the results of the present study, it seems that HIT exercise can lead to a greater increase in muscle growth due to increased TGF-β- dependent myokine, compared to LIT exercise.