Background and Aim: APL is a Prevalent leukemia that Approximately included 5-10% of patients with acute myeloblastic leukemia. ATRA and recently arsenic is used for treatment. ATRA leadsto resistance to treatment and arsenic is toxic in high doses. AZT induce cell death in different ways. The purpose of this study was Assessment of effect of AZT, a telomerase inhibitor, on NB4 cell line (APL cell line) to reduce toxic effect of high dose arsenic.Materials and Methods: In this study, viability and metabolic activityof NB4 cells, treated by different concentrations of AZT (50, 100, 200 mM), was assessed by trypan blue dye method and MTT assay respectively.Results: Treated cells with AZT=50, 100, 200mM showed decreased viability, both in dose-dependent and time-dependent through trypan blue dye method and decreased cell metabolic activity by MTT assay.Discussion and Conclusion: Considering that AZT is able to induce apoptosis and decrease cell activity, it seems AZT is a suitable drug for inhibiting the growth of tumor cells.