Objective To investigate the expression of human telomerase reverse transcripa（se hTERT）, cyclin D1 mRNA, p16INK4, p21WAF1mRNA and p27KIP1 protein in human ameloblastom（a ABs）. Methods The expression of hTERT, cyclin D1, p16INK4, p21WAF1 mRNA and p27KIP1 protein in 54 cases of human ABs were detected by in situ hybridization or immunohistochemistry. Results The positive cases of hTERTmRNA, cyclin D1 mRNA was 51, 23, respectively. The positive cases of p16INK4, p21WAF1 mRNA and p27KIP1 protein was 17, 12, 9. Comparing with recurred and transformed malignantly, the expression of hTERT mRNA, cyclin D1 mRNA increased, and the expression of p16INK4, p21WAF1 mRNA and p27KIP1 protein decreased or lost. The expression of hTERT mRNA and p16INK4, p21WAF1 mRNA and p27KIP1 protein in ABs had middle to high negative relatio（n rk=- 0.587, rk=- 0.652, rk=- 0.783, P
