Manganese ferrte nanopowder was prepared by thermal decomposition at 400℃ of the gel synthesized from manganese and iron nitrates and polyvinyl alcohol.X-ray diffractometry evidenced that manganese ferrite was formed as single crystalline phase at this temperature.Scanning electron microscope images evidenced the formation of very fine spherical particles (d ＜ 11 nm) of manganese ferrite,with specific surface area of 147 m2/g.The powder obtained at 400℃ was used as a catalyst for the oxidative degradation of phenol in aqueous solutions,in the presence of potassium peroxydisulfate as oxidant.High phenol removal efficiencies above 90％ were reached at:pH 3-3.5,phenol initial concentration around 50 mg/L,peroxydisulfate:phenol mass ratio 10∶1,and catalyst dose 3 g/L.Total organic carbon measurements showed that the degradation of phenol goes,under these conditions,to mineralization in an extent of 60％.