Iron/manganese sulfides widely exist 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 through 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 μM 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 S2- 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.