Abstract: Objective: To investigate the effect of arsenic trioxide(As₂O₃) on expressions of matrix metalloproteinase 2 and 9 (MMP-2 and MMP-9) in HL-60 cells. Methods: HL-60 cells were treated with different concentrations of As₂O₃ for 48 hours. Semiquantitative reverse transcription polymerase chain reaction(RT-PCR) was used to examine the expressions of MMP-2 and MMP-9 mRNA. Western blot was used to evaluate the productions of MMP-2 and MMP-9 proteins. Results: The expressions of MMP-2 and MMP-9 mRNA in HL-60 cells were decreased after treated with As₂O₃. There were statistical significances between 5.0 and 7.5 μmol/L As₂O₃ groups and control group(P < 0.05-P < 0.01). The productions of MMP-2 and MMP-9 proteins were reduced dose-dependently when treated with As₂O₃. There was statistical significance between each experimental group and control group(P < 0.05-P < 0.01). Conclusions: As₂O₃ can inhibit the expressions of MMP-2 and MMP-9 in HL-60 cells. This effect might be one of the molecule mechanisms of As₂O₃ in the treatment of leukemia.