MicroRNAs (miRNAs) are 21-25 nt long noncoding RNA that modulate various biological processes, including developmental timing via regulating the expression of their target genes. One critical determinant of normal postnatal lung architecture is septation, and there are many miRNAs involved in the development process. miR-134 is reported as a powerful inducer of pluripotent stem cell differentiation, and we have found that miR-134 is strongly downregulated during mice lung septation (from postnatal Day 2 to postnatal Day 21). Further cell function experiments have revealed that over-expression of miR-134 in A549 and Calu-3 cells can promote cell proliferation and inhibit cell apoptosis and migration abilities in vitro, and the down-expression of miR-134 in cells can act in the opposite way, which indicate that miR-134 is associated with lung septation. This study provides a basis for further investigation of its function in lung development. © The Society for In Vitro Biology 2012.