Abstract: Objective: To investigate the effects of hTERT antisense oligodeoxynucleotide (A-SODN) on the cell cycle and the induction of apoptosis in HL-60 cells. Methods: After treatment with hTERT ASODN the expression of hTERT was assessed by RT-PCR and agarose gel electrophoresis,apoptosis was detected with TUNEL, and cell cycle ratios were determined using flow cytometry (FCM).Results: After 72h of treatment with hTERT ASODN, expression of the hTERT gene was inhibited sig-nificantly (P<0.01). Analysis of the FCM data revealed that the ASODN treated cells were blocked atG₀/G₁ phase and that the number of cells in S phase and G₂/M phase was reduced (P<0.05). The pro-liferation index of the ASODN-treated group was markedly decreased (P<0.05). In the ASODN-treated group the DNA ladder and early apoptosis peak appeared when samples were analyzed by agarose gel electrophoresis and FCM, respectively. Both Annexin V/PI FCM data and TUNEL results indicated that the number of apoptotic cells in the ASODN-treated group was much higher than that found in the SODN-treated group (P<0.01). Conclusion: The hTERT ASODN inhibits expression of the hTERT gene, blocks HL-60 cells at G₀/G₁ phase, induces apoptosis and has a potential therapeutic effect for leukemia.