To evaluate the diurnal and seasonal variations in soil respiration (Rs) and understand the controlling factors, we measured carbon dioxide (CO2) fluxes and their environmental variables using a LI-6400 soil CO2 flux system at a temperate Leymus chinensis meadow steppe in the western Songnen Plain of China in the growing season (May-October) in 2011 and 2012. The diurnal patterns of soil respiration could be expressed as single peak curves, reaching to the maximum at 11:00-15:00 and falling to the minimum at 21:00-23:00 (or before dawn). The time-window between 7:00 and 9:00 could be used as the optimal measuring time to represent the daily mean soil CO2 efflux. In the growing season, the daily value of soil CO2 efflux was moderate in late spring (1.06-2.51 mu mol/(m(2)center dot s) in May), increased sharply and presented a peak in summer (2.95-3.94 mu mol/(m(2)center dot s) in July), and then decreased in autumn (0.74-0.97 mu mol/(m(2)center dot s) in October). Soil temperature (Ts) exerted dominant control on the diurnal and seasonal variations of soil respiration. The temperature sensitivity of soil respiration (Q (10)) exhibited a large seasonal variation, ranging from 1.35 to 3.32, and decreased with an increasing soil temperature. Rs gradually increased with increasing soil water content (Ws) and tended to decrease when Ws exceeded the optimum water content (27%) of Rs. The Ts and Ws had a confounding effect on Rs, and the two-variable equations could account for 72% of the variation in soil respiration (p < 0.01).