Abstract: Nano-NiO powder was prepared by modified sol-gel process.Samples were characterized by thermal analysis and X-ray diffraction.The results indicated that Ni(AC)₂, NH₃H₂O and PEG6000 were used to prepare the sol by the competitive reaction between complexation and hydrolyze.With increase in sintering temperature, nickel contents decreased gradually.Nano-crystalline phase of cubic nickel oxide particles was formed completely until 500 ℃.Eighty-five percent degradation of methyl orange was achieved when the concentration of NiO was 0.4 g/L, illuminating after 4 h with UV lamp of 8 W.