Abstract: The hydrolysis ozone which has strong bactericidal and purification effects has great potential for application inrecirculating aquaculture system (RAS). To investigate the water purification effect of hydrolysis ozone, we constructed a RAS for perches (Lateolabrax japonicus) mainly using hydrolysis ozone treatment during a 120 days' aquaculture period. Wemeasured the effects of different hydrolysis ozone aeration duration (30 min, 60 min, 90 min) on the water quality of the RAS. The results show that: 1) Perches grew well in a high-density aquaculture system, and their mass increased about 4.43 g every day with the final survival rate of 70.22%. No fish diseases were observed during the aquaculture process. 2) Hydrolysis ozone aeration could purify the RAS tail water by effectively removing ammonia nitrogen and nitrite, reducing the biochemical oxygendemand (COD) of tail water, and increasing dissolved oxygen (DO) and pH. Besides, it had less impacts on the increase of total nitrogen content (TN) and nitrate content. 3) The longer the ozone aeration time was, the better the removal effect of COD,ammonia nitrogen, and nitrite in the RAS would be. Under the 90-minute aeration treatment (Ozone mass concentration reached to 0.63 mg·L⁻¹), the removal rates of COD, NH₃-N, and \mathrmNO_2^\text− reached 44.32%, 36.85%, and 79.27%, respectively. Therefore, it is concluded that hydrolysis ozone has a good effect on improving the density of RAS, effectively controlling the occurrence of fish diseases and purifying the tail water of RAS.