To investigate the protective function of antioxidant enzymes against reactive oxygen species(ROS) in nasal polyp formation I measured the activity of superoxide dismutase(SOD), catalase(CAT), and glutathione peroxidase(GSH-Px), one of antioxidant enzymes of human being which detoxify the toxicity of ROS, also measured the superoxide free radical(one of ROS) production, in nasal polyp and control group. The superoxide free radical production and the activity of CAT increased significantly, that of SOD increased without significantly but the activity of GSH-Px decreased significantly. This result indicates that the decreased activity of GSH-Px causes the increase of production of superoxide free radical which may participate in nasal polyp formation. But the cause of increase and decrease of the activity of antioxidant enzymes in nasal polyp is not understood exactly. I think that further study is needed about the direct relationship between antioxidant enzymes and nasal polyp formation.