Background and Objectives: Muscular atrophy is one of the indicators of uncontrolled diabetes. The aim of the current study was to investigate effects of eight weeks of resistance training (RT) on myostatin gene expression in soleus muscles and insulin resistance in streptozotocin (STZ)-induced diabetic rats. Materials and Methods: In general, 14 Wistar male rats weighing 200-250 g and aging 8-10 weeks were selected for the study. Then, a newly prepared diabetic STZ solution was intraperitoneally injected to the rats. Animals were randomly divided into two groups of controls and resistance training diabetes. The resistance training protocol was carried out at ten repetitions as climbing up the ladder with 100% of the body weight for eight weeks, five days a week. Nearly 48 h after the last training session, soleus muscles of the rats were removed and the myostatin gene expression was assessed. Statistical data analysis was carried out using independent t-test at a significance level of P <0.05. Results: Results of the independent t-test showed that the mean expression rate of myostatin protein genes in rat soleus muscles of the resistance training group was significantly lower than that of the control group (P = 0.013). Furthermore, levels of glucose, insulin and insulin resistance were significantly lower in resistance training group, compared to those in control group (P-values of 0.001, 0.005 and 0.001, respectively). A significantly positive correlation was seen between the mean expression of myostatin protein gene and the blood glucose (P = 0.012, r = 0.539), as well as the expression of myostatin protein gene and the insulin resistance (P = 0.015, r = 0.525). Conclusions: Results of this study indicated that resistance training decreased myostatin expression and could improve insulin resistance in rats with type 2 diabetes. Hence, targeting myostatin might be a new therapeutic approach for the treatment of metabolic diseases such as obesity, diabetes and metabolic syndrome.