Lung cancer is a highly malignant carcinoma, and most deaths of lung cancer are caused by metastasis. The alterations associated with epithelial-to-mesenchymal transition (EMT) may be related to the cancer cell metastasis. Nevertheless, the mechanism of lung cancer metastasis remains unclear. We conducted a study in vitro to investigate whether transforming growth factor-β1 (TGF-β1) could induce changes of, such as cell morphology, expression of relative protein markers, and cellular motile and invasive activities. In this research, the changes of cell morphology were first investigated under a phase contrast microscope, then western blotting was employed to detect the expression of E-cadherin, vimentin, and fibronectin, and finally cell motility and invasion were evaluated by cell wound-healing as well as invasion assays. The data indicated that human lung adenocarcinoma cell lines, A-549 and PC-9 cells of epithelial cell characteristics, were induced to undergo EMT by TGF-β1. Following TGF-β1 treatment, cells showed dramatic morphological changes assessed by phase contrast microscopy, accompanied by decreased epithelial marker E-cadherin and increased mesenchymal markers vimentin and fibronectin. More importantly, cell motility and invasion were also enhanced in the EMT process. These results indicated that TGF-β1 may promote lung adenocarcinoma invasion and metastasis via the mechanism of EMT.