DOC (dissolved organic carbon) is a crucial factor for antimony (Sb) enrichment in groundwater. High-Sb groundwater samples were analyzed using hydrochemistry and stable carbon isotope to elaborate the effects of oxidative degradation of organic matter on Sb enrichment in groundwater of Xikuangshan Mines, Hunan. The results indicate that the value of δ¹³ C_DIC and δ¹³ C_DOC ranged from -17.84‰ to -2.30‰ and from -26.87‰ to -16.70‰, respectively. An obviously positive correlation between Sb and DOC, as well as in high - Sb groundwater, indicating that Sb enrichment may be significantly contributed to microbial activities. Meanwhile, DOC had lower values of δ¹³ C compared with dissolved inorganic carbon, suggesting DOC was mainly controlled by endogenous organic matter. Owing to the Sb concentration showed gradually increased trends with decreasing difference between δ¹³ C_DIC and δ¹³ C_DOC, the microbial degradation of DOM had a substantial contribution to Sb mobility.