Superoxide anion (O2-) acts as an exacerbation factor in interstitial pneumonia. Lecithinized-superoxide dismutase (PC-SOD), which is synthesized with a lecithin derivative bound covalently to recombinant human Cu,Zn-SOD, has a longer half-life in plasma and higher affinity to cell membranes than unmodified SOD. The effect of PC-SOD was evaluated using the bleomycin-induced interstitial pneumonia mouse model. Treatment with PC-SOD at 10 mg/kg significantly reduced the hydroxyproline content and fibrosis score. Namely, PC-SOD suppressed the progression of pulmonary fibrosis on the bleomycin-induced interstitial pneumonia mouse model. PC-SOD may be a potential drug for interstitial pneumonia therapy.