This study is to investigate therapeutic effect of astaxanthin on acetic acid-induced gastric ulcer in rats.  Rats were divided into control group, ulcer control group, and astaxanthin (5, 10, and 25 mg·kg^-1) groups at random, 8 rats in each group.  After administered for 10 days consecutively, all the rats were sacrificed.  The area of ulcer and the levels of MDA, SOD, CAT and GSH-Px in gastric mucosa were measured.  Compared with ulcer control group, in astaxanthin (5, 10, and 25 mg·kg^-1) groups, the area of ulcer was decreased significantly.  Level of MDA decreased while activities of SOD, CAT and GSH-Px increased (P < 0.05).  Astaxanthin has good therapeutic effect on acetic acid-induced gastric ulcer in rats.  Eliminating free radical and improving local blood circulation of the ulcer may be the mechanism of action.