Abstract: Manganese oxide （Mn3O4） powder were prepared by precipitation-oxidation method with manganese sulfate and aqueous ammonia as raw materials，and air and ammonium nitrate as oxidants.The phase，morphology，and average particle diameter of the as-prepared samples were characterized by means of XRD，FT-IR，and SEM etc..The hydrolysis process of manganese sulfate in the aqueous ammonia as well as the process of manganese hydroxide being oxidized into Mn3O4 in liquid phase were studied.Especially，the effects of oxidation temperature，oxidation time，and drying on the oxidation process were mainly investigated.Results showed that the formation of manganese hydroxysulfate can be reduced through negative-adding manganese sulfate dropwise into the aqueous ammonia（positive adding is：putting  ammonia into manganese sulfate solution）， and ammonium nitrate adding in solution accelerated the reaction rate of manganese hydroxide oxidized by solved air.The electronic grade Mn3O4 particles with high purity，fine granularity，and low sulfur content were obtained when ammonium nitrate of 3 g was added（the mass ratio of ammonium nitrate to manganese sulfate was about 1∶7.5），oxidation temperature of 70 ℃，maintaining 4 h in solution，and then air drying for 4 h.

Key words: manganese sulfate, Mn3O4, precipitation-oxidation, oxidant