Abstract 【Objective】Soil erosion is a serious problem, causing soil and nutrient losses and altering physical, chemical and biological properties of the soil. Numerous reports have been published on effects of soil erosion on soil physicochemical properties. However, little has been done on quantitative analysis of how soil erosion and deposition affect soil microbial biomass in the black soil region of China. Soil microbial biomass is a sensitive indicator of changes in the environment, compared with soil organic matter. The study on impacts of soil erosion and deposition on soil microbial biomass is expected to be able to provide certain important basis for scientific evaluation of the environmental effects of soil erosion. Therefore, the study was oriented to investigate response of soil microbial biomass carbon and nitrogen to soil erosion and deposition, by analyzing soil microbial biomass carbon, microbial biomass nitrogen and erosion rate of the soils at different locations (the upper stream, middle stream and downstream reaches) in the valley and different positions (the upper, middle, and lower slope position) on a slope. 【Method】The Binzhou River Valley, a typical region of black soil thin in soil layer in Northeast China, was taken as the research area. Contents of microbial biomass carbon and microbial biomass nitrogen in the soils of the sampling sites different in slope position and location in the valley were measured using the chloroform fumigation extraction method and erosion rates of the soils estimated using the ¹³⁷Cs tracer method. 【Result】Results show significant differences exist between the soils in spatial distribution of soil microbial biomass, and negative relationships of the spatial distributions of soil microbial biomass carbon and microbial biomass nitrogen with that of soil erosion and deposition. On the watershed scale, soil erosion rate declined drastically from the upper stream down to the middle stream and the lower stream, while both soil microbial biomass carbon and microbial biomass nitrogen exhibited a reverse trend, being significantly higher in the downstream than in the upper stream and middle stream. The content of soil microbial biomass carbon was 26.9% and 17.4% lower, respectively, in the upper stream and the middle stream than in the downstream, and the content of soil microbial biomass nitrogen 22.9% and 18.1% lower. On the slope scale, soil erosion rate descended significantly from the middle slope position to the upper slope position and to the lower slope position; but both soil microbial biomass carbon and microbial biomass nitrogen acted reversely, too, beingsignificantly higher at the lower slope than at the middle slope. The content of soil microbial biomass carbon was 13.8% and 20.2%, respectively,lower at the upper slope and the middle slope than at the lower slope, and the content of soil microbial biomass nitrogen 10.0% and 19.5% lower. Regression analysis shows that the contents of soil microbial biomass and nutrient decreased linearly with increasing soil erosion rate. Microbial biomass carbon, microbial biomass nitrogen, organic matter and total nitrogen in the soil were negatively related with soil erosion rate at an extremely significant level (p <0.01), respectively. 【Conclusion】Obviously soil erosion has some profound impacts on spatial distributions of the microbial biomasscarbon and microbial biomass nitrogen in the soil. The removal and redistribution of soil nutrients caused by the processes of soil erosion and deposition is the main reason why spatial distribution of soil microbial biomass differ between erosion and deposition areas.