Abstract: Objective This study is to investigate the therapeutic effect and mechanism of ATO treated EAU in rats. Methods EAU models were induced in 25 SPF female Lewis rats aged 6 weeks by the injection of interphotoreceptor retinoid-binding protein(IRBP)to planta and ATO was administrated by intraperitoneal injection at a does of 5 mg/(kg•d)、2mg/(kg•d) or 0.5mg/(kg•d) respectively for 15 days in 5 model rats,and 2 mg/(kg•d) of cyclosporine A(CsA) was used at the same way in CsA group,and normal saline solution was injected in 5 model rats as positive control group.EAU was assessed under the slitlamp biomicroscopy every day and histological score of retinas was evaluated on day 15 after immunization. Weight of rats of all groups were recorded before and after experiment. The infiltration of T-bet+Th1 cells and FOXP3+Treg cells was detected by immunochemistry. Results The congestion of iris vessels,fibrous exudates and retroiridal hypopyon were found in the rats of ATO 0.5mg/(kg•d) group and normal saline solution．However，mild inflammatory response at ocular anterior segment was seen in the rats from CsA group and ATO 5mg/(kg•d) group under the slim lamp．The obvious congestion of iris vessel，fibrous exudates and mild retroiridal hypopyon are found in the rat of ATO2mg/(kg•d) . The clinical score was significantly lower in ATO 5mg/(kg•d) 、ATO 2mg/(kg•d) and CsA group compared with normal saline solution group(P =0.000、P =0.004 and P =0.008), The clinical score was significantly lower in ATO 5mg/(kg•d) compared with ATO 2mg/(kg•d)（P =0.046）. The retinal histopathological score showed significant difference among CsA group、ATO 5mg/(kg•d)、ATO 2mg/(kg•d) group and normal saline solution group(F=31.75，P =0.000) . The histopathological score was significantly lower in CsA group、ATO 5mg/(kg•d) and ATO 2mg/(kg•d) group compared with normal saline solution group(P =0.000、P =0.000 and P =0.000).There were no significant difference among the weight of all groups after experiment( P >0.05). The exudation of T-bet+Th1 cells was apparently decreased in 5mg ATO group，2mg ATO group and CsA group in comparison with normal saline solution group，and the numbers of FOXP3+Treg cells in retina were similar in all groups. Conclusion Intraperitoneal injection of ATO 5mg/(kg•d) is effective in suppressing the ongoing process of EAU by inhibiting infiltration of T-bet+Th1