Abstract: Objective To investage the effects of Fructus Psoraleae and dihydroartemisinin on expression of CD28,pathological change of intestine in mice infected with Cryptosporidium parvum.Methods Cryptosporidium parvum infection was induced by hypodermic injection of dexamethasone in mice,twice a week for 4 weeks.Sixty mice were divided into 5 groups in random:A(normal group),B(control group),C(therapeutic group of Fructus psoraleae),D(therapeutic group of dihydroartemisinin),E(therapeutic group of the two agents combination).According to the period of therapy(1 or 2 weeks),therapeutic groups were subdivided into A1,A2,B1,B2,C1,C2,D1,D2,and E1,E2.Results Compared with the control group,the number of Crypatosporidium parvum oocysts in feces were decreased obviously in all treatment groups(P<0.05).The pathological damage of intestinal epitheliums were renovated after therapeutic treatment.Proportions of CD28 T lymphocytes in peripheral blood in all treatment groups were higher than those of infected control groups(P<0.05).Conclusion Fructus psoraleae and dihydroartemisinin are effective in the treatment of cryptosporidiosis in mice.Dihydroartemisinin can remarkably eliminate Cryptosporidium parvum.Fructus psoraleae can up-regulate peripheral blood CD28 and proportion of CD4⁺ and CD3⁺ T cells.The two agents participate in the host immune response and inflammatory reaction with synergic effect and ultimately restore inflammatory responce.