Objective To observe the effect of dexamethasone on tumor growth and angiogenesis in mouse H 22 model. Methods H 22 cells were injected subcutaneously into BALB/c mice. Drug treatment began from the day of inoculation (first group) or from the fourth day after inoculation (second group). Tumor's diameters were measured every day. In the twelfth day mice were sacrificed and tumors were weighed. Tumor microvessel count was performed by immunohistochemical staining and flow cytometry assay with anti-CD31 monoclonal antibody. Results Tumor growth was inhibited by dexamethasone significantly in both groups. Both tumor weight and final tumor volume of the treatment were smaller than the control, P<0.05, and the rates of inhibition were 31.48% and 35.38% in the first and second group respectively. In first group, the tumor microvessel count decreased significantly vs control, P<0.01; in the second group, tumor microvessel count was reduced too, but it had no markedly difference compared with control. Conclusions Dexamethasone inhibits tumor growth in mouse H 22 model significantly. The inhibition may be correlated with the anti-angiogenic effect of dexamethasone, but when tumor has already grown to certain size, the efficacy is limited.