Due to their diversity and abundancy, marine resources have emerged as important biological resources to compensate the limited sources of terrestrial biological materials. Phaeodactylum tricornutum (PT) is one of classical model diatoms most widely studied for its ecology, physiology, biochemistry and molecular biology. In this study, four different PT extracts on lipopolysaccharide (LPS)-stimulated macrophages were compared for anti-inflammatory effect and investigated for the underlying mechanisms. The extracts of PT inhibited nitric oxide production from LPS stimulated RAW 264.7 cells in a dose dependent manner. These extracts also inhibited the expression of mRNA and production of proteins of pro-inflammatory cytokines such as interleukin (IL)-$1{eta}$, IL-6 and tumor necrosis factor-${alpha}$. These inhibitory effects were found to be caused by blockage of nuclear factor-${kappa}B$ activation and phosphorylation of p38 mitogen-activated protein kinases, extracellular signal-regulated kinases 1 and 2 and c-Jun N-terminal kinase.