Using La2O3 and Co(NO3)2•6H2O as raw material, ultrafine perovskite-type oxides LaCoO3 was prepared by Supercritical Fluid Drying Technology and Sol-Gel method. The prepared materials’ crystal structure and morphology were characterized by TG-DTA、XRD、FT-IR and TEM. The photocatalytic activity of ultrafine LaCoO3 powders was evaluated by degradation of methyl orange (MO) solution under 15W UV light irradiation. The results show: At 250°C , the amorphous ultrafine La-Co particles with the size less than 10 nm can be obtained by Supercritical Fluid Drying Technology. At 850°C , the size of the particles increased to 15-35nm, the nanocrystalline LaCoO3 had a perfect rhombohedral perovskite structure. At 900°C , the crystalline phases of the lanthanum-cobalt mixed oxides were LaCoO3 and La2O3, and the amorphous component is Co2O3, the presence of lanthanum affects the crystallization of cobalt oxides. The LaCoO3 has excellent photocatalytic activities and 100% MO solution was decolorized only after 4h.