In this study, we found that DHA not only markedly decreased the mRNA and protein expression levels of metastasis-associated enzymes, such as MMP1, MMP2, MMP7 and MMP9, but also significantly downregulated the expression of EMT-related or regulatory genes, such as vimentin, β-catenin, N-cadherin, Snail, Slug, and Zeb1, in NSCLC cells. The gene discussed is SNAI1; the disease is non-small cell lung carcinoma.