In order to study photo-Fenton performance of Fe₃O₄ nanospheres, monodispersed Fe₃O₄ nanospheres with a mean diameter of 200 nm were successfully synthesized by a solvothermal method at 200 ℃. As-synthesized Fe₃O₄ nanospheres show excellent photo-Fenton efficiency on the degradation of methylene blue(MB), and the degradation rate was over 95%. Besides, the catalyst was easy to recycle with only a piece of magnet, and the recovery rate can be more than 85%. Moreover, the catalyst can be regenerated with the ultrasonic treatment, and the degradation performance almost remains unchanged. In addition, the degradation efficiency varies with the amount of hydrogen peroxide applied and the pH value of the reaction system. After intensive investigation, the reaction efficiency performs best with 15 mL hydrogen peroxide added in acid atmosphere.