Root biomass exponential regression method was used to distinguish root respiration from soil microbial respiration in a Leymus Chinensis steppe in the Xilin River Basin of Inner Mongolia, China. The contribution of root respiration to soil respiration averaged (24 +/- 3)%, ranging from 13%-52%; while the contribution of microbial respiration to soil respiration averaged (76 +/- 3)%, ranging from 48%-87%. Correlation between soil respiration and root biomass was relatively unstable. Root respiration vitality decreased exponentially with the ratio of root to shoot biomass (R2 = 0.661, P = 0.20), while it increased exponentially with soil water content at 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm (P < 0.0001). CO2 released by root respiration and the contribution of root respiration to soil respiration increased exponentially with root respiration vitality (R = 0.848, P = 0.01; R2 = 0.818, P = 0.01, respectively).