BACKGROUND: Bronchopulmonary dysplasia (BPD) is a chronic lung disease of preterm neonates; the underlying pathogenesis is not fully understood. MicroRNAs (length 21-25 nucleotides) are ribonucleic acid (RNA) molecules that have important functions in development, cellular differentiation, apoptosis, proliferation, and migration; very little is known regarding their role in developmental lung diseases. METHODS: We exposed neonatal mice to either room air or 60% oxygen, beginning at birth, and we used microRNA microarray and real-time polymerase chain reaction on lung samples. RESULTS: The hyperoxia-exposed mice developed a lung injury that mimicked human BPD. Fifty-one microRNAs shared similar profiles in the hyperoxia-exposed BPD lungs and the normal lungs, which indicates that those microRNAs might play a protective role during the septation process. In the BPD lungs, compared to the control lungs, 14 microRNAs were up-regulated, and 7 microRNAs were down-regulated, which indicates that these microRNAs might play an important role in the development of BPD. Some of the candidate microRNAs can regulate cell proliferation. CONCLUSIONS: To our knowledge, this study is the first to identify microRNAs associated with BPD development, which provides a clue for further investigation of their function in BPD development. © 2011 Daedalus Enterprises002E.