Introduction: Studies have shown a strong relationship between physical activity and the presence of cardiovascular risk factors such as hypertension, insulin resistance, diabetes, dyslipidemia and obesity that characterize the metabolic syndrome. Moreover, the practice of regular physical activity has been recommended for the prevention and treatment of this syndrome. Objectives: The aim of this study was to analyze by histomorphometric techniques, the effect of aerobic exercise in the soleus muscle of rats with metabolic syndrome. Methodology: A total of 15 male Wistar rats, 150 days old, divided into three groups (n = 5): sedentary, control (C); metabolic syndrome (MS) and trained, metabolic syndrome (TMS). The induction of MS was performed using fructose in the drinking water of animals. From the 9th week of induction, animals in the Training groups underwent exercise treadmill belt (Imbramed TK-01) with moderate intensity (50-70% of maximum speed achieved in the stress test). Physical training was conducted for nine weeks, with a frequency of 5 times per week, for about 60 minutes. The procedures were approved by the Ethics Committee of the São Judas Tadeu University (protocol Nr 060/2007). At the end of the experiment the animals were euthanized by decapitation. The right soleus muscle was sectioned, fixed and treated for conducting conventional histology, and the slides stained by HE and Picrosirius methods. Photomicrographs of 10 fields per animal were captured by light microscope, transferred to the image analysis program (Software Axio Vision, Zeiss). We measured the cross-sectional areas of muscle fibers and to analyze the volume densities of muscle fibers, capillaries, and interstitial collagen fibers, was used stereological method (252 points). The statistical analysis used was ANOVA One Way and Tukey test (p < 0.05). Results: The MS group showed a significant decrease in the cross section area of the muscle fibers, the volume density of the fibers, and increased capillary and interstitial collagen fibers. With training there was an increase in the volume density of collagen fibers, interstitial and capillary. Conclusion: Our data show that the metabolic syndrome causes changes in the soleus muscle in all parameters studied and that aerobic exercise of moderate intensity was not able to minimize major changes caused by metabolic syndrome.