In order to verify the anti-inflammatory effects of Gelidium amansii, RAW264.7 macrophages were incubated with the extract of 70% ethanol solution (Ex), and activated with the endotoxin lipopolysaccharide (LPS). Ex inhibited the expression of the pro-inflammatory enzymes, including inducible nitric oxide (NO) synthase (iNOS) and cyclooxygenase-2 (COX-2), and the production of iNOS-mediated NO and COX-2-mediated prostglandin $E_2$ ($PGE_2$) production in a dose-dependent manner. Ex also reduced the release of the pro-inflammatory cytokines, including tumor necrosis factor-${alpha}$ (TNF-${alpha}$), interleukin-1${eta}$ (IL-1${eta}$) and IL-6 in LPS-activated macrophages, The observed anti-inflammatory effects of Ex was associated with inactivation of the nuclear factor ${kappa}B$ (NF-${kappa}B$) that mediates the induction of iNOS, COX-2, TNF-${alpha}$, IL-1${eta}$, and IL-6. Further studies showed that Ex inactivated NF-${kappa}B$ through inhibition of phosphorylation of the inhibitory ${kappa}B$ ($l{kappa}B$), Taken together, these results suggest that Gelidium amansii exerts anti-inflammatory effects by inhibiting the expression of pro-inflammatory enzymes and the secretion of pro-inflammatory cytokines via inactivation of NF-${kappa}B$ and/or $l{kappa}B$.