To understand the effects of geomorphology and environment on the ¹³C character of soil organic carbon (SOC) in a hilly karst area, 26 soil samples were collected in 2008 in Nanchuan, Chongqing, SW China. The results showed that the δ¹³C-SOC values were between -18.66‰~-27.41‰, with the mean value of -23.3‰. The data firmly indicated that the modern soil organic carbon was the mixture of C3 and C4 plants and mainly originated from C3 plants rather than C4 plants. According to the sequence of δ¹³C-SOC along the geomorphological change at this hilly karst area, it can be seen that the δ¹³C-SOC values was the crest > brae > foot. Based on the results of correlation analysis, the positive correlation between the δ¹³C-SOC values and their altitude is 0.432 (p=0.028), which reflects the land/soil degradation effects caused by the hilly geomorphology, especially in the water and soil erosion process.