Objective To investigate the effects of red orpiment on cell morphology, expression of promyelocytic leukemia (PML) mRNA and its protein localization in NB4 and HL-60 cell lines.Methods Cell morphology was assayed by Wright’s staining and fluorescence staining, while PML mRNA expression was determined by RT-PCR. PML protein localization by evaluated by immunofluorescence staining. Results The typical apoptosis was found in NB4 and HL-60 cells after treatment with red orpiment. The fusion protein was no longer observed in NB4 cells, PML protein was relocated, and then degraded. In HL-60 cells, PML protein underwent a similar progress. The expression of promyelocytic leukemia (PML) mRNA was not changed in the treated cells.Conclusion Red orpiment inhibits the proliferation of leukemia cells by inducing them to undergo apoptosis. Objective To investigate the effects of red orpiment on cell morphology, expression of promyelocytic leukemia (PML) mRNA and its protein localization in NB4 and HL-60 cell lines. Methods Cell morphology was assayed by Wright’s staining and fluorescence staining, while PML mRNA expression was determined by RT-PCR. PML protein localization by evaluated by immunofluorescence staining. Results The typical apoptosis was found in NB4 and HL-60 cells after treatment with red orpiment. The fusion protein was no longer observed in NB4 cells, PML protein was relocated, The expression of promyelocytic leukemia (PML) mRNA was not changed in the treated cells. Conclusion Red orpiment inhibits the proliferation of leukemia cells by inducing them to undergo apoptosis. In HL-60 cells, PML protein underwent a similar progress.