Background: Melatonin as an antioxidant agent can have an effective role in lung development. In this study, the effect of melatonin administration on lung injury in the neonate mice was assessed. Materials and Methods: Lung injury was induced by two injections of 15 mg/kg methylazoxymethanol (MAM) on gestational day 15 (E15). Pregnant BALB/c mice were randomly divided into five groups: Control (CO), Melatonin (MEL), Luzindole (Luz), MAM, and MAM+MEL. Melatonin and luzindole were intra-peritoneally injected at a dose of 10 mg/kg (from E15 until delivery). Histopathological changes including: hemorrhage, neutrophils infiltration and fibrosis in the neonate lung were studied by hematoxylin and eosin (H&E) and Masson’s Trichrome staining. Alveolarization and alveolar wall thickness were measured. Results: In histological examination, hemorrhage, neutrophils infiltration and fibrosis were seen in the MAM and Luz groups; however, these injuries were attenuated in the MAM plus melatonin group. Significant reduction of alveolarization was recorded in the MAM and Luz groups compared to the control group, while the alveolar wall thickness was significantly increased in these groups compared to control group. Conclusion: Administration of exogenous melatonin in pregnant mice could have a protective effect on the pulmonary development of neonates and could decrease lung injury in neonate mice.