The alpine region in the Tibetan Plateau, characterized by sharp contrasts in topographpy and bioclimate, accounts for about one-fifth of China’s total land area. Due to limited field observation and high spatial heterogeneity, distribution of soil organic and inorganic carbon in the alpine region remains unclear. A better understanding of the distributions of soil organic and inorganic carbon and their controlling factors in this region is critical for accurate assessment of terrestrial carbon storage and important in implication for dealing with global climatic change. In this study, investigations were conducted of vertical distribution of soil organic and inorganic carbon along two toposequences in the middle Qilian Mountains on the northeastern edge of the Tibetan Plateau, one on the shady or north slope, the Hulugou watershed and the other on the sunny or south slope, the Shitougou watershed. Each toposequence consists of five typical soil profiles, and soil samples were collected by soil genetic horizons. The objectives of this study were to examine changes in vertical distribution of soil organic and inorganic carbon along the two toposequences, and to identify main controlling factors for the variations of soil organic and inorganic carboncontent at the slope scale in a relatively small region. Results show that organic carbon content decreased with soil depth in both toposequences, but the rate was much higherin the sunny slope (66% to 91%) than in the shady slope (31% to 77%). In the soil profiles along the shady slope, inorganic carbon was found distributed quite evenly (< 5.0 g kg^-1) due to the strong leaching of carbonate, while in the soil profiles along the sunny slope, inorganic carbon in B horizons was two-fold as high as that in A horizons, which demonstrates that evident enrichment of inorganic carbon in the B horizons of the soil profiles on the sunny slope. Soil carbon in the topmost 1 meter soil layer did not vary much in density between the north and south slopes (16.1 to 33.9 kg m^-2 and 11.8 to 32.8 kg m^-2 respectively), but did in composition. In the north slope, the soil carbon was dominated by organic carbon accounting for 82% to 99% in density, however, the soil organic and inorganic carbon in the south slope varied sharply in density, accounting for 27% to 81% and 19% to 73% of the soil total, respectively. Therefore, it may be concluded that slope aspect plays an important role in the vertical distribution as well as composition of soil carbon in the alpine region. In addition, precipitation and vegetation are also major factors affecting spatial variability of soil carbon along the toposequences. With the mean annual precipitation increasing by 1 mm, soil organic carbon within the 0~20 cm soil layer increased by 0.4 g kg^-1, while inorganic carbon within the 40~80 cm soil layer declined by 0.2 g kg^-1. And vegetation type also had some effect on enrichment of soil organic carbon. All the findings in this study demonstrate that the study on soil carbon cycling and the estimation of soil carbon stocks in the alpine region should take into account the influence of micro-topography, especially slope aspect, on distribution, composition and spatial variation of soil carbon at the slope scale.