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Grazing exclusion is regarded as an effective way to restore degraded grasslands. However, it remains unclear if grazing exclusion could improve soil bacterial communities and how the soil bacteria affect soil organic carbon (SOC) in semi-arid grasslands over 33 years of continuous grazing exclusion. We studied the effects of 33 years of grazing exclusion on vegetation characteristics, soil properties, and the soil bacterial communities in the semi-arid grasslands. Our results showed that grazing exclusion significantly increased species diversity and richness, coverage, above- and belowground biomass and litter biomass. Total nitrogen (TN), soil organic carbon (SOC), total phosphorus (TP), soil available potassium (AK), and soil available phosphorus (AP) significantly increased. Grazing exclusion also improved the diversity and abundance of soil bacteria, which had a significant positive correlation with SOC. The dominant taxonomic groups of soil bacteria in grazed and grazing exclusion grasslands included Actinobacteria, Proteobacteria, Acidobacteria, Firmicutes, Planctomycetes, Chloroflexi, Gemmatimonadetes and Bacteroidetes. There was an interaction between SOC, TN, AK, AP and the relative abundances of some dominant groups. Long-term grazing exclusion had a negative effect on diversity and the abundance of soil bacteria. Our results may provide new insights for grassland management in the semi-arid regions. (C) 2016 Elsevier B.V. All rights reserved.