Abstract: Objective To investigate the effect of ³²P irradiation on the cell cycle of HL-60 cells. Methods Flow cytometry was employed to detect cell cycle changes of HL-60 cells induced by ³²P irradiation at different doses for varied time lengths(24, 28 and 72 h, respectively). Result ³²P could induce cell cycle arrest in S and G₂/M phases, and the arrest occurred initially in G₂/M phase. Conclusion ³²P may significantly interfere with the cell cycle of HL-60 cells, causing cell cycle arrest primarily in G₂/M.