In the present study, we investigated the anti-inflammatory effects by kaempferol-3-O-${eta}$-D-sophoroside (KS) isolated from Sophora japonica (Leguminosae) on the lipopolysaccharide (LPS)-induced nitric oxide (NO) and prostaglandin ($PGE_2$) production by RAW 264.7 cell line compared with kaempferol. KS significantly inhibited the LPS-induced NO and $PGE_2$ production. Consistent with these observations, KS reduced the LPS-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) at the protein and mRNA levels in a concentration-dependent manner. In addition, the release and the mRNA expression levels of tumor necrosis $factor-{alpha}$ ($TNF-{alpha}$) and interleukin-6 (IL-6) were also reduced by KS. Moreover, KS attenuated the LPS-induced activation of nuclear factor-kappa B ($NF{-kappa}B$), a transcription factor necessary for pro-inflammatory mediators, iNOS, COX-2, $TNF-{alpha}$ and IL-6 expression. These results suggest that the down regulation of iNOS, COX-2, $TNF-{alpha}$, and IL-6 expression by KS are achieved by the downregulation of $NF{-kappa}B$ activity, and that is also responsible for its anti-inflammatory effects.