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Elucidating the generation mechanism of reactive oxygen species (ROS) is essential for advanced oxidation processes with respect to environmental and biological sciences. Herein, self-generation of ROS such as hydroxyl radicals (·OH), superoxide radicals (O 2 •-) and singlet oxygen (1O 2) from the interaction between multi-layered flowerlike MoS 2 nanosheets and H 2 O 2 is presented. The results demonstrate that H 2 O 2 can exfoliate multi-layered MoS 2 into quantum dots and promote a 2H to 1 T phase change accompanied by the dissolution of MoS 2 to produce H+, MoO 4 2− and SO 4 2−. Electron spin resonance (ESR) spectroscopy confirm the production of ·OH, superoxide radicals O 2 •- and 1O 2 in the MoS 2 /H 2 O 2 system. The calculation data based on density functional theory (DFT) indicate that the 1 T-MoS 2 can lower the free energy profiles for stepwise catalytic decomposition of H 2 O 2 to produce ROS as compared to 2H–MoS 2. • H 2 O 2 is decomposed into reactive oxygen species (ROS) over MoS 2. • MoS 2 is exfoliated and experiences a 2H to 1 T phase transition. • ·OH, O 2.•- and 1O 2 are the dominating ROS by the interaction between MoS 2 and H 2 O 2. • 1 T-MoS 2 can lower the free energy profiles for stepwise decomposition of H 2 O 2. • The degradation of methyl orange (MO) can probe the oxidation ability of ROS. [ABSTRACT FROM AUTHOR]