Docosahexaenoic acid (DHA) is rich in fish oil with many pharmacological impacts such as anti-inflammation and anti-cancer activities. In the present study, we aimed to investigate the inhibitory effects of DHA on the invasion and inflammation in prostate cancer cells. The cytotoxicity of DHA with or without lipopolysaccharides (LPS) treatment was evaluated by MTT assay. The invasion and wound healing assays were used to determine the roles of DHA in cell migration and invasion after LPS treatment. The expression levels of IL-6 and IL-8 were detected using ELISA assay. The protein expression was investigated by Western blotting. DHA exhibited significant cytotoxicity at the concentration of 100 μM in PC3 cells. Exposure to DHA (6, 12 and 25 μM) dose-dependently inhibited invasion and wound closure potential in PC3 cells after LPS treatment. DHA dose-dependently downregulated LPS-induced expression levels of IL-6 and IL-8. In addition, the LPS-induced protein levels of p-AKT and COX-2 were suppressed by DHA treatment. Our results indicate that low doses of DHA effectively inhibit metastasis by decreasing IL-6, IL-8, p-AKT and COX-2 expression levels after LPS treatment.