Abstract: Objectivc To observe effects of antisense human telomer ase RNA(hTR) on telomeric length (TRF) and telomerease activity of human gastr i c cancer cell SGC7901. Methods SGC7901 cell line was transfecte d with antisense hTR expression vector(pBBS-hTR) by lipofectamine,and expressio n s of hTR,telomere and telomerase activity in the gene transfected cells were det ected by hybridization of nucleic acids and a telomeric repeat amplification protocol(TRAP). Results Clones containing antisense or control p lasmi d s were selected 3 weeks after transfection by HyR selection and either antisen se hTR expression had been enhanced or sense hTR expression had been inhibited 72h after transfection by specific stained RNA probe.Telomerase activity and mean T RF length were general low in the gene transfected cells in comparision with t ho se in the control plasmid transfected cells. Conclusion Antisen se hTR may either control TRF length by blocking the template region of hTR or s erve as a effective target for treating gastric cancer by inhibiting telomerase .