In this study, the MnFe2O4@Co3S4 magnetic nanocomposite was prepared by a two-step hydrothermal method and used to catalyze the ozone oxidation degradation of methylene blue. It was characterized by XRD, EDS, SEM, FT-IR, and XPS. The results showed that the introduction of Co3S4 made MnFe2O4 grow uniformly on Co3S4 nanosheets, which effectively prevented the agglomeration of MnFe2O4. Moreover, MnFe2O4 provided active sites and Mn3+/Mn2+ and Fe3+/Fe2+ cycles for the ozone oxidation process. Not only did Co3S4 provide the active site (Co2+/Co3+) for the ozone oxidation process but also its derived S2-/S22- accelerated the electron transfer rate on the surface of the material, thus improving the efficiency of catalytic ozone oxidation degradation of methylene blue. When the molar ratio of MnFe2O4 to Co3S4 was 6:3 (MnFe2O4@Co3S4-3), the catalytic ozone degradation efficiency of methylene blue was the best, which reached 93.55% in 12 min. The reactive oxygen species in catalytic ozonation degradation of MB were 1O2, O2.-, and ·OH. The MnFe2O4@Co3S4 magnetic nanocomposite is an efficient and stable O3 activator, which maintains high catalytic activity and low metal ion leaching after five cycles, indicating that it has a good application prospect in catalyzing ozone oxidation to degrade organic pollutants.