Abstract： Objective To investigate the role of matrix metalloproteinases(MMP- 2, MMP-9 ) in the pathogenesis of acute lung injury induced by hyperoxia.Methods Seventy-two mice were exposed in sealed cages with >95% high concentration oxygen (for 24-72 hours) or room air. The expression and activity of MMP-2 and MMP-9 in bronchoalveolar lavage fluids (BALF) and lung tissues at 24. 48 and 72 hours of hyperoxia were studied by gelatin zymography, reverse transcriptpolymerase chain reaction and immunohistochemistry.Result Acute lung injury caused by hyperoxia was accompanied with increased expression and activity of MMP-2 and MMP-9 in BALF, an upregulation of MMP-2, MMP-9 mRNA and protein in lung tissues.Conclusion MMP-2 and MMP-9 play an important role in the development of hyperoxia-induced acute lung injury in mice.