Aim: This study intented to clarify the intracellular effect of PAI-1 on Non-small cell lung cancer (NSCLC) metastasis and the precise mechanism involved. Methods: The metastatic properties of NSCLC cells were determined by transwell assays and wound healing assay in vitro. The mRNA and protein expressions of genes were analyzed by Real-time qPCR and western blot, respectively. Pulmonary metastasis model of NSCLC cells was established to evaluate the pro-metastasis effect of PAI-1 and anti-metastatic effect of miR-34a in vivo. The gene targets of miR-34a were confirmed by luciferase reporter assays. Chromatin immunoprecipitation assay was employed to detect the transcriptional regulation of miR-34a. Co-immunoprecipitation assay was performed to observe the interaction of proteins. Results: PAI-1, which was elevated in NSCLC patients with recurrence and metastasis, augmented NSCLC metastasis and was negatively related to the prognosis of NSCLC. miR-34a, which was decreased in NSCLC patients with metastasis, attenuated NSCLC metastasis and was positively correlated with the prognosis of NSCLC. Moreover, PAI-1 was identified as the target gene of miR-34a and activated the Stat3 signaling pathway to promote epithelial-mesenchymal transition (EMT) in NSCLC cells. PAI-1 interacted with PIAS3 to regulate Stat3-dependent gene expression and miR-34a was transcriptionally suppressed by Stat3 to form a positive regulatory loop through Stat3 signaling. Conclusion: Our findings suggest that PAI-1 and miR-34a, which can be clinically utilized as biomarkers for the clinical prognosis or diagnosis of NSCLC, are potential targets for the treatment of NSCLC. (C) 2017 Elsevier Inc. All rights reserved.