A huge amount of soil organic and inorganic carbon (SOC and SIC) is stored in soils and those stored carbon (C) plays an important role in affecting the global climate change. Knowledge on the spatial distribution of and land management effects on soil C in the Eurasian steppes is essential for understanding its impact on the global climate change. We investigated both the distribution of SOC and SIC contents and the effect of land cultivation on SOC content across a transect of continental steppes in Inner Mongolia, including the western plateau and the eastern plain. There were weak increasing trends in SOC and SIC from west to east across the transect. In general, SOC decreased but SIC increased with increasing soil depth. Both SOC and SIC were markedly different among various land uses in the Xilin River basin, approximately located in the center of the studied continental steppes. Grasslands and meadows together accounted for 93.9 and 98.1%, respectively, of the total SOC and SIC storages in the basin, whereas wetlands played an insignificant role in soil C storage due to both their small area and sandy soil texture. Land cultivation caused losses of 7.7 and 18.1% of SOC in the 0–10 cm soil layer on the western plateau and the eastern plain, respectively. The loss of SOC mainly occurred in the coarse-size fraction (> 0.25 mm) in the surface 0–10 cm soil layer. Sandy soil texture, low mean annual temperature and infrequent land cultivation somewhat limited the loss of SOC in the continental steppes.