Non-small cell lung cancer (NSCLC) accounts for 80%-90% of all lung cancers. The metastasis of NSCLC has a considerable impact on prognosis and systemic status. Cycloalliin, an organosulfur compound found in garlic, is known for its health benefits on cardiovascular disease and obesity. However, the role of cycloalliin in cancer cell invasion and metastasis remains unknown. In this study, we investigated the effect of cycloalliin on the epithelial-to-mesenchymal transition (EMT) and invasiveness of the NSCLC cell line A549. Cycloalliin inhibited transforming growth factor (TGF)-β-induced EMT and invasive potential of A549 cells. Furthermore, we found that cycloalliin suppressed Smad3 phosphorylation and expression of Snail, a transcription factor that promotes EMT, during the early stages of TGF-β-mediated EMT. This study provides valuable insights into the inhibitory potential of cycloalliin on EMT, suggesting that this compound may have a therapeutic role against EMT in NSCLC cells.