OBJECTIVE: Vascular endothelial growth factor (VEGF) contributes to lung development and recovery of lung structure from lung injury. This study aimed to explore the changes of expression of VEGF protein and mRNA in neonatal rats following hyperoxic lung injury. METHODS: Forty-eight Sprague-Dawley neonatal rats were randomly continually exposed to hyperoxia (FiO2=95%) or to room air (FiO2=21%, control group) 30 minutes after birth. VEGF protein and mRNA expression in the lungs was determined by immunohistochemical methods and reverse tanscription polymerasechain reaction (RT-PCR) respectively 3,7 and 14 days after birth. RESULTS: VEGF protein and mRNA expression increased with increasing postnatal age in the control group. In the hyperoxia exposure group VEGF protein expression decreased markedly at 7 days (7.79±5.23 vs 12.67±3.82; P<0.01) and 14 days of hyperoxia exposure (5.85±3.37 vs 15.10±8.91; P<0.01) compared with the controls. VEGF mRNA expression in the hyperoxia exposure group was significantly reduced from 3 days (0.78±0.22 vs 1.19±0.63) through 14 days of hyperoxia exposure (0.48±0.12 vs 1.89±0.81) compared with the controls (P<0.01). CONCLUSIONS: VEGF is associated with lung development in neonatal rats. Hyperoxia exposure can decrease VEGF protein and VEGF mRNA expression in the lungs of neonatal rats. VEGF might be involved in the pathogenesis of hyperoxic lung injury.