Objective: To study the expression of CD34 and vascular endothelial growth factor (VEGF) in human ameloblastoma (AB) and odontogenic keratocyst (OKC). Materials and Methods: Specimens from78 cases of AB (including 36 cases of primary AB, 35 cases of recurrent AB, and 7 examples of malignant AB), 18 cases of OKC, and 4 examples of normal oral mucosa were examined by the sterptovidin-biotin method using anti-CD34 monoclonal antibodies. Expression of VEGF was detected in 70 cases of AB, 33 cases of OKC and 7 examples of normal oral mucosa by immunohistochemistry. MVD (microvessel density) was counted in CD34-positive vessels. Results: CD34 expression was extensively positive in AB cases. In malignant AB, catenuliform vessels appeared around invasive tumor cells or were sleeved by tumor cells. In benign AB, vessels were extensively scattered or appeared in clusters around the invasive tumor cells. Immunoreactivity for CD34 suggested that vascular development was related to cell differentiation; vessels were extensively scattered or appeared in clusters around the invasive tumor cell. Immunoreactivity for CD34 suggested that vascular development was related to cell differentiation; vessels were rarely found around keratotic or degraded cells. MVD increased gradually in primary, recurrent and malignant AB (P < 0.001). Comparing AB with OKC and normal oral mucosa, there was a significant difference in MVD (P < 0.001). VEGF expression was significantly associated with MVD, having the same expression pattern. Conclusions: Vascular development in tumors is related to cell differentiation and the biological characteristics of AB and OKC tumors.