144 soil samples were collected along the moisture gradient in grassland region of the Mongolian Plateau for investigating soil microbial biomass C(C_mic)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.C_mic ranged from 51.7 to 797mg kg^-1;Nmic from 11 to 118.6mg kg^-1;C_mic:Nmic from 5 to 9,and C_mic/C_org from 1.15% to 4.1%.C_mic/C_org 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(Q_CO2) with precipitation can fit in quadratic equation.Effect of grazing on soil microbial biomass depends on grassland types and grazing intensity.