Abstract: A grazing experiment was conducted in two alpine steppe meadows (winter pasture and summer pasture) and one alpine meadow (summer pasture) in Northern Tibet in July 2008. The phospholipid fatty-acid (PLFA) method was used to characterise the soil microbial community. Fungi, gram-negative bacteria, actinomycetes and protozoa in ungrazed soils were significantly higher than grazed soils in winter pasture on the alpine steppe meadow. Total PLFA, fungi, bacteria, gram-positive bacteria, gram-negative bacteria, actinomycetes, arbuscular mycorrhizal fungi and protozoa in the ungrazed soils were also significantly higher than those of grazed soils in the summer alpine meadow. There were significant differences in soil microbial community structure between ungrazed and grazed soils for all three alpine grasslands based on redundancy analysis. Soil inorganic nitrogen and dissolved organic nitrogen significantly affected the variation in the soil PLFA profile in the alpine steppe meadow for the winter pasture, whereas nitrate nitrogen and dissolved organic carbon significantly affected the variation of soil PLFA profile for the summer pastures. Our findings suggested that clarifying the effect of grazing on alpine soil microbial communities needs to consider grazing season and grassland types in Northern Tibet.