Pedogenic carbonates (PCs) are important components of the soil carbon (SC) pools in arid and semi-arid regions, and the pool of PCs is 2 ~ 5 times bigger than that of soil organic carbon therein. Formation and turnover of the PCs plays a significant role in balance of soil carbon in the regions. Soil samples were collected from a Stipa breviflora dominated desert steppe in Inner Mongolia for analysis of content and δ¹³C of soil carbonates，δ¹³C of CO₂ and δ¹³C of parent rocks, hence to explore effect of formation and turnover of pedogenic carbonates on sequestration of CO₂ and calculate the amount of CO₂ sequestrated. Results show that the δ13C value of PCs was determined mainly by the composition of carbonate isotopes of soil CO₂ and could be figured out with the aid of the δ¹³C value of soil CO₂. Fractionation of the SC in the study area revealed that PCs accounted for 83.6%, 65.4%, 41.7% and 17.4% in the soil layers of 40-50, 50-60, 60-80 and 80-100 cm, respectively. With the help of δ13C values and the principles in chemical balance, the amount of CO₂ sequestrated during the process of PCs formation and turnover was worked out, being 38.3, 39.2, 25.1 and 9.2 g kg ^-1 soil in these layers, respectively.