Abstract:144 soil samples were collected along the moisture gradient in grassland region of the Mongolian Plateau for investigating soil microbial biomass C(Cmic)and N(Nmic),and their relations to annu al average temperature and rainfal.The results are as followings:Soil microbial biomass C and N showed significant correlations with soil organic carbon,total nitrogen,precipitation,and tempera ture.Cmic ranged from 51.7 to 797mg kg-1;Nmic from 11 to 118.6mg kg-1;Cmic:Nmic from 5 to 9,and Cmic/Corg from 1.15% to 4.1%.Cmic/Corg was correlative negatively with soil organic C, total N,and annual average precipitation.Soil respiration showed a decreasing trend:meadow steppe>typical steppe>desert steppe,correlating positively with precipitation,and negatively with temperature.The relationship of metabolic quot ient CO2(QCO2) with precipitation can fit in quadratic equation.Effect of grazing on soil microbial biomass depends on grassland types and grazing intensity.