Perovskite oxides ErFeO₃ was a new-style photocatalytic material. Using Er(NO₃)₃.5H₂O, Fe(NO₃)₃×9H₂O, citric acid and urea as the main materials, the ErFeO₃ gel was prepared by sol-gel process. Then, the gel was dried in the 80℃ air oven for 48 hours. The xerogel was calcined in the muffle furnace at the temperature of 700-1000℃for preparation ErFeO₃samples. The samples were characterized by thermogravimetric and differential scanning calorimetry (TG-DSC), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance spectra (DRS). Using methyl orange as waste water, the photocatalytic activity of ErFeO₃ was studied under visible-light. The results showed that the particle size of perovskite structure ErFeO₃ was about 80-100 nm and the gap width was about 2.0 eV. Under visible-light, ErFeO₃ showed the high visible-light photocatalytic activity for the decomposition of methyl orange. The ErFeO₃ photocatalysts which were prepared by sol-gel process had wide application prospect in sewage treatment under visible-light.