Low molecular weight phenolic acids (LMWPAs) are active components of natural organic matter (NOM), whose redox reactions may exert substantial influence on the speciation and mobility of trace metals in soils. The mechanism of the interactions between NOM and antimony (Sb) was previously unraveled under sunlight, while remained poorly understood in the absence of light. In our study, the combination of wet chemistry, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) based calculations were applied to explore the mechanism of Sb(III) oxidation induced by various LMWPAs and their effect on Sb(III) adsorption on goethite in the dark. The results indicated that Sb(III) was rapidly oxidized to Sb(V) in the presence of LMWPAs in neutral and alkaline conditions. The reactive oxygen species (hydrogen peroxide) and quinone species (the semiquinone radical and oxidized forms of LMWPAs) were the main contributors to the oxidation. According to DFT based calculations, the bond dissociation enthalpy (BDE) of the phenolic hydroxyl groups is well correlated with the Sb(III) oxidation rate constant, which is in line with its pro-oxidant property towards Sb(III) through the production of semiquinone radical. The significant inhibition of Sb adsorption on goethite as the pH increased was observed. Except for the competitive adsorption by LMWPAs, the inhibition also resulted from the extensive Sb(III) oxidation in the suspension and the lower Sb(V) sorption capacity of goethite at higher pH. Besides, the edge-sharing inner-sphere complexes were formed between Sb and goethite regardless of the presence of LMWPAs. The findings of this study provided new insights into the role of LMWPAs in Sb(III) oxidation and their profound effect on Sb immobilization by iron minerals.