Objective: To investigate the effects of DFMO on the growth characteristics, apoptosis and activity of telomerase of K562 cells. Methods: The growth rate, phase distribution of cell cycle and apoptosis of treated cells with DFMO were detected by cell count, morphological assay, FCM analysis and DNA electrophoresis, respectively. The telomerase activity was examined by telomeric repeat amplification protocol(TRAP). Results: In K562 cells treated with DFMO, the growth rate was markedly retarded. The increase in G1 -phase cells and decrease in s-phase population and induction of apoptosis were observed. The activity of telomerase of treated cells was inhibited. Conclusion: The growth inhibition and apoptosis induction of K562 cells treated by DFMO were associated with suppressed telomerase activity. It is suggested that inactivation of telomerase in cancer cells conld be one of important events in antitumor molecular mechanism of inhibition of polyamine biosynthesis.