The effects of grazing on nitrogen cycle bacteria, nitrogen fixation, ammonification and nitrification were studied in Leymus chinensis steppe in Inner Mongolia. The results showed that light grazing increased significantly the amounts of four types of nitrogen cycle bacteria and the intensities of soil nitrogen fixation, ammonification and nitrification, and promoted the circulation of soil nitrogen, but heavy grazing produced the converse trend. Grazing intensity had no significant effect on the seasonal variation of nitrogen cycle bacteria, nitrogen fixation, ammonification and nitrification.