In order to study the antioxidant enzyme activity of hippocampal tissue in the rat model of Alzheimer's Disease (AD) carrying abnormal savda syndrome and observe the effect and mechanism of prescription on the oxidative stress, 36 male Wistar rats are randomly divided into six groups (six rats per group). A rat model combining disease with syndrome is established, three days latter, three groups are given Yihei (abnormal savda) granula for 15 days. The spectrophoto-metric method is employed to test the activity of SOD, GSH-Px, CAT, MAO and the content of MDA in the hippocampus of rat cerebrum. It is found that.the activity of SOD, GSH-Px, and CAT is obliviously decreased, the activity of MAO and the content of MDA is significantly increased in the rat hippocampus of the model group, compared with the normal group, the difference is significant (P<0.01). After the treatment, the group given high dose of Yihei granula demonstrates that the activity of SOD, CAT, GSH-Px (P<0.01) increase, and the activity of MAO, content of MDA are decreased in rat hippocampus (P<0.01). Compared with the model group, the difference is significant (P<0.01), However, compared with Donepezil group, there is insignificant difference between these two groups (P>0.05). The group given mild dose of Yihei granula demonstrates that the activity of SOD increases, compared with the model group, the difference is significant (P<0.01). The activity of GSH-Px, CAT is increase, the activity of MAO is decrease, compared with the model group, the difference is significant (P<0.05), the content of MDA does not improve obviously, compared with normal group, the difference is insignificant (P<0.01). The group given low dose of Yihei granula is compared with the model group, there is insignificant difference in the activity of SOD, CAT, MAO, and the content of MDA(P>0.05). Compared with normal group, the difference is significant (P<0.01). There is significant difference in the activity of GSH-Px compared with model group (P<0.05). Therefore, the rat model combining disease with syndrome does an injury to free radical, oxidative stress is excessive, and Yihei granular is able to improve the activity of antioxidant enzyme, reduce the content of MDA, and inhibit the incidents of AD by antioxidative effect. It might be one of the formula mechanisms for the AD treatment.