Abstract: The physical fractionation method was used to measure the contents of soil particulate organic carbon (POC) and particulate organic nitrogen (PON) in eight grassland sites along an elevation gradient on the Helan Mountain, Inner Mongolia. The relationships of POC, PON and their proportion with vegetation characteristics and environmental factors were analyzed. Both POC and PON declined significantly with altitude and with soil depth. Meanwhile, POC and PON changed significantly among vegetation types. The proportions of POC and PON reduced considerably with the altitude from 2 940 to 1 820 and 1 700 m. Among the four vegetation types, proportions of both POC and PON were the highest in the alpine meadow and lowest in the desert steppe. The proportions of POC and PON had significant positive correlations with vegetation cover, aboveground plant biomass and mean annual precipitation, but a significant negative correlation with mean annual temperature.