The present study evaluated the corporal development, plasma testosterone profile, and  morphological/biochemical aspects of skeletal muscle after treatment with nandrolone decanoate and/or high-intensity resistance exercise in adult rats. The animals received 5 mg/Kg of nandrolone decanoate or vehicle, twice a week/6 weeks and/or were exposed to high-intensity resistance exercise-training. The training protocol consisted of 25 jumps sessions, for 6 weeks (5 days/week). The anabolic steroid and training isolated were not effective in change body mass while the association anabolic steroid plus training reduced the body mass at the end of the experimental period. The plasma testosterone was reduced in  high-intensity resistance exercise-trained group compared to untrained one. The training protocol and the training plus treatment with nandrolone decanoate decreased the fiber area pattern of both soleus and extensor digitorum longus muscles. In soleus muscle an increase in MHC total was observed in rats treated with nandrolone decanoate in relation to trained rats. In conclusion, the anabolic steroid and the high-intensity resistance exercise might isolated or in association modulate body mass, testosterone level, and morphological and biochemical aspects of some types of skeletal muscle of rats. In spite of that, in the association steroid and training the effects are always detected.