Abstract: Waste water containing acid red B (ARB) was treated with Y₂O₃/WO₃. The reaction mechanism of photocatalysis was studied. The relations of the composition and amount of heterogeneous photocatalyst, pH value of solution, H₂O₂ amount and illumination time with the decolorizing rate of ARE were discussed, The results showed that the decolorizing rate of ARB could reach 99.3% by using Y₂O₃/WO₃ as heterogeneous photocatalyst with the Y₂O₃ mass fraction of 3.0% in Y₂O₃/WO₃, 50mL of 20mg·L^-1 ARB (initial concentration), the catalyst mass of 0.4 g, pH 6.0, the H₂O₂ amount of 7.35 mmol·L^-1, and the illumination time of 6 h.