Iron/manganese sulfides exist widely in the anoxic underground environment. The element cycling process of Fe, Mn and S controls the material cycling and energy conversion process in the underground environment. Usually, iron sulfides can produce reactive oxygen species (ROS) with O₂ disturbance by providing electrons to reduce O₂. However, the specific mechanism of ROS production by the reaction between manganese sulfides and O₂ is still unclear. Herein, manganese sulfide (MnS), a prevalent natural form of manganese sulfide minerals, was studied to explore the species, kinetics and reaction mechanisms of ROS generated by the activation of O₂ by MnS. The results showed that MnS could activate O₂ to produce a large number of ROS, including ·OH, H₂O₂ and O₂^·-. The maximum cumulative ·OH reached 389.0 μmol/L using 1 g/L MnS with initial pH 3 at 200 r/min stirring speed, and the yield of ·OH was 4.4 and 149.6 times greater than that of FeS and FeS₂ oxygenation under the same molar concentration, respectively. The reduction of O₂ by MnS resulted in the generation of O₂^·- through the transfer of single electron, followed by the acquisition of an additional electron to form H₂O₂. The dissolved Mn²⁺ catalyzed O₂/H₂O₂ to produce ·OH with low efficiency, but the structural Mn(II) could efficiently catalyze H₂O₂ to produce abundant ·OH, indicating that heterogeneous catalysis of H₂O₂ played an important role in ·OH production. Additionally, the soluble S^2- might facilitate electrons transfer to high-valence Mn(Ⅲ)/Mn(Ⅳ) to promote the regeneration of structural Mn(Ⅱ), which further promoted the production efficiency of ·OH via strengthening the electron cycle of Mn(Ⅱ)/Mn(Ⅲ). Furthermore, the degradation efficiency of phenol (5 mg/L) by MnS/O₂ system was up to 97.4% within 3 h, indicating that the activation of O₂ by MnS showed great potential in the environmental remediation.