Smoking is a risk factor for idiopathic pulmonary fibrosis (IPF), but the mechanism of the association remains unknown. The aim of this study was to investigate the effects of cigarette smoke extract (CSE) on A549 cells and human lung fibroblasts treated with transforming growth factor-beta1. A transwell two-chamber coculture system was used to study the proliferation, differentiation, morphologic changes and soluble factors production of A549 cells and myofibroblasts. Low concentrations of CSE promoted myofibroblasts proliferation; however, high concentrations of CSE inhibited their proliferation. Low concentrations of CSE also markedly increased extracellular secretion of hydrogen peroxide, inhibited proliferation, induced apoptosis and produced epithelial-mesenchymal transition (EMT) in cocultured A549 cells. This cigarette smoke-induced A549 cells EMT may become a new pathophysiological concept in the development of IPF. CSE possibly takes part in the development and progress of IPF by increasing oxidative stress.