The aim of this study was to investigate the effects of an acute bout of exhaustive resistance exercise on the expression of myogenesis modulators (Myostatin (MSTN) and MyoD) in male trained and untrained wistar rats’ fast and slow muscles. Thirty rats were assigned to three groups: control (n=6), untrained (n=12) and trained (n=12). Resistance exercise (weight lifting up a vertical ladder) was administered to the trained group while other groups received to exercise. 48 hours after the last training session, trained and untrained groups performed an acute bout of exhaustive resistance exercise and were sacrificed three (n=6) and six hours (n=6) following the session. MSTN and MyoD expressions were measured in SOL and FHL muscles by Real time – PCR technique and data were analyzed via 2-??CT method. The differences between variables were determined by independent t test. The expression level of MyoD in SOL, 3 and 6 hours after the last session of training in trained group decreased 1.54 times and increased 1.07 times. In untrained group, it decreased 2.86 and 4 times respectively. The expression level of MyoD in FHL, 3 and 6 hours after the last session of training in trained group increased 70 and 339 folds. In untrained group, it increased 193 and 206 times respectively. No data were found for MSTN of the trained group in SOL. For untrained group 3 hours after a session of an acute exercise, the expression of MSTN of SOL decreased 854 times while no data were found 6 hours after a session. In addition, 3 and 6 hours after the last session of training, the expression of MSTN decreased 15.87 and 1.39 times respectively in FHL of the trained group. The expression of MSTN of untrained group 3 and 6 hours after exercise increased 59 and 151 times respectively in FHL. The findings revealed different responses of MyoD and MSTN to one bout of exhaustive resistance exercise in fast and slow twitch skeletal muscles of trained and untrained rats.