In this work, the Er 3+:YAlO 3 as an up-conversion luminescence agent was prepared by sol–gel and auto-combustion method. And then the Er 3+:YAlO 3/TiO 2 composite, a novel sonocatalyst, was successfully synthesized by sol–gel method. The key influences such as amount of coating Er 3+:YAlO 3, heat treatment temperature and heat treatment time on the sonocatalytic activity of Er 3+:YAlO 3/TiO 2 composites, as well as the amount of Er 3+:YAlO 3/TiO 2 on the sonocatalytic degradation of organic dye was studied. The results indicated that the sonocatalytic activity of TiO 2 could be enhanced obviously by coating Er 3+:YAlO 3. When 1.0 g/L Er 3+:YAlO 3/TiO 2 composite with 50 wt.% amount of coated Er 3+:YAlO 3 and mixed crystal of TiO 2 film was adopted, the highest degradation efficiency was obtained. In addition, the effect of 1-butanol as OH scavenger on the degradation was studied. It showed that the degradation of Acid red B was mainly caused by hydroxyl radical oxidation. Finally, the sonocatalytic degradation of some other organic dyes revealed that the Er 3+:YAlO 3/TiO 2 composite was a widely useable sonocatalyst in treating various dye wastewaters.