Objective:To investigate the effect and the mechanism of cordycepin on inhibiting delayed type hypersensitivity.Methods:The mouse model of delayed type hypersensitivity was established by sensitizing the skin of Kunming mice with 2,4-dinitrochlorobenzen(2,4-DNCB). There are two experimental groups respectively treated with different dosages of cordycepin:12 mg/kg and 16 mg/kg and one negative control group treated with normal saline. All the mice were intraperitoneally injected at 24 h interval(the last interval was 4 hours). We calculated the differences of the thickness and the weight between the left and right earlaps of every mouse and the edema rate, then used statistical methods to compare the edema rate and the spleen index among all the groups. After HE staining, the pathological changes of inflammatory earlap and spleen were observed and compared among these three groups.Results:Cordycepin alleviated the erythema, edema and the infiltration of peripheral mononuclear cells in the earlaps, so lowering the differences of the thickness and weight between left and right earlaps in the experimental groups. But it showed no significant effects on the spleen index and the spleen pathological changes. Compared with that in the negative control group, the anti-inflammatory effects of cordycepin in two experimental groups showed significant differences(P