Abstract: Objective To investigate the effects of hyperoxia on the expression of lung heme oxygenase-1 (HO-1) in rat pups. Methods 21-d-old male Sprague-Dawley rat pups were randomly divided into 5 groups: room-air control group and 12, 24, 48, 72 hours hyperoxia groups. The rat pups were continuously exposed to oxygen (92%～94%) and room-air respectively. The left lung wet/ dry weight ratio and the histological examination were performed. The expressions of lung HO-1 mRNA and HO-1 protein were also measured by RT-PCR and Western blot, respectively. Results The expressions of lung HO-1 mRNA in 12 hours hyperoxia group (0.35±0.043) and HO-1 protein in 24 hours hyperoxia group (0.455±0.046) were increased as compared to those in the room-air group (0.263±0.037, 0.28±0.044), and the increases were more significant with the longer hyperoxia exposure (P < 0.05, P < 0.01). Compared with the room-air control, the left lung wet/ dry weight ratio and the lung injury scores were significantly increased in 48 hours hyperoxia group and 72 hours hyperoxia group (P < 0.05, P < 0.01). Conclusion Hyperoxia can induce the increase of lung heme oxygenase-1 expression in rat pups.