Docosahexaenoic acid, an important long-chain, polyunsaturated omega-3 (n−3) fatty acid, significantly inhibited invasion and metastasis of NSCLC cells, and concomitantly downregulated the expression of metastasis- and EMT-related genes and p-STAT3 signaling pathway. The gene discussed is STAT3; the disease is non-small cell lung carcinoma.