Background: Alpha lipoic acid (alpha-LA) is a naturally occurring antioxidant and metabolic enzyme cofactor. Recently, alpha-LA has been reported to inhibit the growth of various cancer cells, but the precise signaling pathways that mediate the effects of alpha-LA on non-small cell lung cancer (NSCLC) development remain unclear. Methods: The CCK-8 assay was used to assess cell proliferation in NSCLC cell lines after alpha-LA treatment. The expression of growth factor receptor-bound protein 2 (Grb2), cyclin-dependent kinase (CDK)-2, CDK4, CDK6, Cyclin D3, Cyclin E1, Ras, c-Raf, epidermal growth factor receptor (EGFR), ERK1/2 and activated EGFR and ERK1/2 was evaluated by western blotting. Grb2 levels were restored in alpha-LA-treated cells by transfection of a plasmid carrying Grb2 and were reduced in NSCLC cells via specific siRNA-mediated knockdown. Results: alpha-LA dramatically decreased NSCLC cell proliferation by downregulating Grb2; in contrast, Grb2 overexpression significantly prevented alpha-LA-induced decrease in cell growth in vitro. Western blot analysis indicated that alpha-LA decreased the levels of phospho-EGFR, CDK2/4/6, Cyclins D3 and El, which are associated with the inhibition of G1/S-phase transition. Additional experiments indicated that Grb2 inhibition partially abolished EGF-induced phospho-EGFR and phospho-ERK1/2 activity. In addition, alpha-LA exerted greater inhibitory effects than gefitinib on NSCLC cells by preventing EGF-induced EGFR activation. Conclusion: For the first time, these findings provide the first evidence that alpha-LA inhibits cell proliferation through Grb2 by suppressing EGFR phosphorylation and that MAPK/ERK is involved in this pathway. (C) 2017 Published by Elsevier Inc.