An animal model with decreasing SOD was established by fever from intravenous injection of endotoxin. The SOD level was measured by RIA in the animal serum and liver tissues. The results indicated that the SOD level of the model group was obviously lower than that of the normal group (P < 0.05), but the level of the group treated with Semen Ziziphi Spinosae was higher than that of the model group. The study shows that Semen Ziziphi Spinosae can protect mice with endotoxin fever from SOD decrease.