The fluorescence components of dissolved organic matter (DOM) is a crucial controlling factor in mobilizing antimony in groundwater. However, the effect of molecular composition of DOM on Sb behaviors is still unclear. A total of 10 samples were collected from high-and low-Sb groundwater in the Xikuangshan mine to compare the molecular composition of DOM and to determine the roles of DOM in Sb mobility. The results show that the DOM content in high-and low-Sb groundwater was 2.24 ~ 10.45 mg/L(mean 5.19 mg/L) and 3.22 ~ 3.23 mg/L(mean 3.23 mg/L), respectively. Compared with low-Sb groundwater, high-Sb groundwater has more highly unsaturated and phenolic compounds and polyphenols, and lower aliphatic compounds, saturated compounds and polycyclic aromatics. Sb positively associated with high O/C ratio (O/C > 0.5) and low H/C ratio molecules (H/C < 1.2), which mainly grouped as highly unsaturated and phenolic compounds and polyphenols. Complexing agents with Fe and Sb(V), competitive adsorption with Sb(V), and accelerating the rate of Sb(Ⅲ) and Fe(Ⅱ) co-oxidation were considered as the formation mechanisms for DOM on Sb migration at a molecular level.