Objective To investigate the effects of sodium selenite on telomerase activity and expression of hTERT mRNA in cadmium-transformed 16HBE cells. Methods Telomerase activity and expression of genes were measured after cultured cadmium-transformed 16HBE cells were exposed to sodium selenite at different doses (0.625, 1.25, 2.50, 5.00 μmol/L) for 24 hours. Results Selenium decreased telomerase activity in cadmium-transformed 16HBE cells. There existed an obvious dose-effect relationship between the selenium concentration and these changes. The expression of hTERT and c-myc mRNA also decreased but the expression of mad1 mRNA increased after exposure to selenium for 24 hours. No difference was found in expression of hTRF1 and hTRF2 mRNA after incubated with sodium selenite for 24 hours, compared with control group.Conclusion Selenium inhibits telomerase activity by decreasing hTERT and c-myc mRNA expression and increasing mad1 mRNA expression in cadmium-transformed 16HBE cells and selenium concentration is significantly correlated with these changes.