Introduction: Epithelial to mesenchymal transition (EMT) relates to both organ fibrosis and malignant behavior of cancer. Pirfenidone (PFD) is an anti-fibrotic agent for idiopathic pulmonary fibrosis and one of its functions may be to inhibit fibrotic EMT. This study aimed to investigate the possibility that PFD might exert an anti-tumor effect through inhibition of EMT in non-small cell lung cancer (NSCLC) cell lines in vitro and in vivo. Methods: NSCLC cells (A549, NCI-H358) were used to evaluate PFD effects on TGF-131 induced phenotypic changes. Possible TGF-I31 signaling pathways modulated by PFD were evaluated. The effects of PFD on EMT induced by an anti-cancer drug was also analyzed. The impact of PFD on tumor growth in nude mice as well as on EMT change in vivo was also determined. Results: PFD significantly inhibited TGF-I31-induced EMT. Smad2 phosphorylation and TGF-I31 receptor I expression were also inhibited as was translocation of Smad2 from the cytoplasm into the nucleus. Carboplatin induced elevation of TGF-I31 production from cancer cells together with induction of EMT, which were suppressed by co-treatment with PFD. In in vivo examination, PFD alone did not inhibit tumor progression whereas its combination with carboplatin significantly decreased tumor growth. Immunohistological analysis showed that PFD suppressed EMT change induced by carboplatin. Conclusions: PFD could attenuate the EMT process induced not only by exogenous TGF-81 but also by paracrine TGF-8 produced from NSCLC cells. PFD may be a promising new therapeutic agent for the treatment of NSCLC through the regulation of EMT. (C) 2017 Elsevier B.V. All rights reserved.