The effect of antisense hTERT mRNA oligodeoxynucleotide on telomerase activity of leukemia cells was explored and investigated in the present study. Telomerase activity was measured by the telomerase PCR ELISA assay kit (TRAP); hTERT mRNA expression by reverse transcription polymerase chain reaction (RT-PCR) assay and gel-image system, hTERT protein by immunochemistry and flowcytometry. Results showed Incubation of leukemic cells (HL-60 and K562 cell lines) with 10 mol/l AS PS-ODN would significantly reduce the their mRNA levels and in vitro expression of hTERT protein 24 h later, so that the telomerase activity would be significantly down-regulated or inhibited. In conlusion, the hTERT AS PS-ODN is an excellent inhibitor for telomerase activity.