There are contested views on the effects of grazing on soil carbon. A study was done to assess the effect of grazing and other controlling factors on soil organic carbon in arid and semiarid rangelands. Five rangeland sites were selected for sampling. Each rangeland was divided into three grazing intensities: ungrazed, moderately grazed, and severely grazed. In each region, plots were randomly placed and their vegetation and environmental factors were measured. Soil samples were taken from 0- to 30-cm depths in each plot. The differences in soil carbon content between different rangeland sites and also different grazing intensities were tested. Principal component analysis (PCA) was used to determine the main environmental factor controlling soil organic carbon. The results showed significant differences between different rangeland sites in soil carbon content, although there were no significant differences between different grazing intensities. So, it can be concluded that factors other than grazing are effective on soil carbon content. The results of PCA revealed that vegetation cover, climatic factors, parental material, and elevation are the main environmental factors controlling soil carbon content in arid and semiarid rangelands.