There was upward trend in alveolar chord length and cell apoptosis while downward trend in positive expression rate of Ki67 and CD31 proteins in BPD mice treated with miR-29a antagomir as compared to the mice exposed to RA following miR-29a antagomir treatment (p < 0.05). The gene discussed is MKI67; the disease is bronchopulmonary dysplasia.