The expression of P27 protein was investigated in 40 cases of odontogenic tumors by immunohistochemical S-P assay. The results showed that P27 expression varied in different types of odontogenic tumors. Positive signals were present in 17/20 (85.0%) of the malignant odontogenic tumors, but in 6/20 (30.3%) of the benign ones (P < 0.005). It was suggested that P27 protein had certain practical value in the differentiation diagnosis of odontogenic tumors.