BACKGROUND Oxygen toxicity mediated by reactive oxygen species (ROS) plays an essential role in the development of bronchopulmonary dysplasia in premature infants. By reducing oxidative stress, antioxidants protect the immature lung. We studied the effects of MnTBAP, a catalytic antioxidant on angiogenesis and alveolar growth following neonatal hyperoxia. METHODS Newborn mouse litters randomized to room air (RA) or >95% O2 for 72 hours from day 4 (D4) to D7 to receive either MnTBAP (10 mg/kg/d) or saline intraperitoneally (every 24 h for three doses). Lungs harvested for angiogenic gene expression, protein expression, and histopathology post-hyperoxia exposure. Radial alveolar count (RAC), mean linear intercept (MLI) and vessel density assessed by histopathology. RESULTS Angiogenic gene expression was significantly lower in the hyperoxia group compared to the RA group. The protein expression for VEGF and its receptor, VEGFR1, was significantly lower following treatment with MnTBAP compared to hyperoxia alone. Expression of VEGFR2, Angiopoietin-1 and TIE2, were substantially higher in the RA groups compared to hyperoxia groups with or without MnTBAP. Hyperoxia groups demonstrated alveolar simplification. MnTBAP reduced vessel density and failed to improve alveolar growth following hyperoxia. CONCLUSIONS MnTBAP, a catalytic antioxidant, does not offer protection from hyperoxia-induced alveolar impairment. The lack of angiogenic upregulation by MnTBAP may contribute to alveolar simplification in newborn mice.