Recent studies have underscored the importance of grasslands as potential carbon (C) sinks. We performed a grazing experiment with seven stocking rates (SR0, SR1.5, SR3.0, SR4.5, SR6.0, SR7.5, and SR9.0 for 0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep ha-1, respectively) to investigate the effect of increasing grazing pressure on soil C and nitrogen (N) storage in the temperate grasslands of northern China. The results revealed that C and N storage in both 0-10 cm and 10-30 cm soil layers decreased linearly with increasing stocking rates. Carbon storage in the 0-10 cm soil layer was significantly higher in lightly grazed grasslands than in heavily grazed grasslands after a 5-yr grazing treatment. Our findings suggest an underlying transformation from soil C sequestration under light grazing to C loss under heavy grazing, and that the threshold for this transformation is 4.5 sheep ha-1 (grazing period from June to September). Results confirmed that grasslands used for grazing in northern China have the capacity to sequester C in the soil under appropriate grazing pressure, but that they lose C under heavy grazing. Therefore, appropriate grazer densities will promote soil C sequestration in the grasslands of northern China.