OBJECTIVE:The aim of present study was to investigate the expression of telomerase hTR gene in oral precancerous lesion and squamous cell carcinoma. METHODS:82 cases were detected by in situ hybridization technique for hTR gene,including 7 cases of normal oral mucosa,7 cases of hyperplasia lesions,30 cases of oral precancerous lesions(dysplasia lesion),38 cases of oral squamous cell carcinomas.RESULTS:Weaker signal of hTR gene expression was observed in normal oral mucosa and hyperplasia lesions,positive cell were present in basal layer,hTR positivity was 28.56%(4 of 14).The expression of hTR gene in the precancerous lesions was gradually strong associated with phenotypic progression and the degree of dysplasia;positive cell extended from basal layer to multi layered epithelium,hTR positivity was 60%(18 of 30).Strong hTR expression was observed in squamous cell carcinoma,the positivity was 81.58%(31 of 38).CONCLUSION:Telomerase is activated frequently during the late stage of oral precancerous lesion and may play a crucial role in oral squamous cell carcinogenesis.