Abstract: Soil microbial biomass C, N in brown soil and several different particle fractions of microaggregates extracted from it of different land use types were studied with the fumigation-extraction method. The results show: (1) The contents of microbial biomass C, N in brown soil keep in the same trend, <10μm >the original soil>10~50μm>50~250μm. With multiple comparison of it, except the difference between the original soil with the 10~50μm microaggregates, others difference is obvious evidently. Soil microbial biomass C, N in forestland is the highest, which in cultivated land is the lowest. The effects of the different land use types to the contents of microbial biomass C, N were significant. (2) The ratios of BC/TC and BN/TN of original soil, <10μm, 10~50μm in natural forest was lowest. The organic matter input of different land use types is difference of qualities, which cause the result.