Abstract: To investigate the relationship between DNA methylation and the expression of human telomerase reverse transcriptase (hTERT) in normal liver L02 cells and hepatocellular carcinoma cell line SMMC- 7721 and to study the effect of demethylation induced with 5' - aza- dC by observing hTERT expression and telomerase activity. Methods: The methylation pattern of hTERT in cell lines was assayed by methylation- specific PCR (MSP). Demethylation in cultured cells was induced by adding 5' - aza- dC. The expression of hTERT was measured using RT- PCR and telomerase activity was detected by TRAP- ELISA. Results: In the L02 cells the hTERT promoter was methylated and the cells had decreased hTERT expression, while the expression level of hTERT was much higher in the SMMC- 7721 cells. The expression of hTERT was upregulated and telomerase activity was increased in L02 cells after demethylation. Conclusion: hTERT expression may be repressed by methylation of its promoter, and abnormal demethylation of the hTERT promoter may play an important role in the development of hepatocellular carcinoma.