To investigate the efficacy and the mechanism of the anti-inflammatory effect of Taraxacum officinale leaves (TOLs), the effect of a methanol extract and its fractions recovered from TOLs on lipopolysaccharide (LPS)-induced responses was studied in the mouse macrophage cell line, RAW 264.7. Cells were pretreated with various concentrations of the methanol extract and its fractions and subsequently incubated with LPS ($1{mu}g/mL$). The levels of nitric oxide (NO), prostaglandin (PG) $E_2$, and pro-inflammatory cytokines including tumor necrosis factor (TNF)-${alpha}$, interleukin (IL)-$1{eta}$, and IL-6 were determined using enzyme-linked immunosorbent assays. Expressions of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 and activation of mitogen-activated protein (MAP) kinases were analyzed using western blotting. The methanol extract and its fractions inhibited LPS-induced production of NO, pro-inflammatory cytokines, and $PGE_2$ in a dosedependent manner. The chloroform fraction significantly suppressed production of NO, $PGE_2$, and two pro-inflammatory cytokines (TNF-${alpha}$ and IL-$1{eta}$) in a dose-dependent manner with 50% inhibitory concentration values of 66.51, 90.96, 114.76, and $171.06{mu}g/mL$, respectively. The ethyl acetate fraction also inhibited production of the inflammatory molecules. The chloroform and ethyl acetate fractions reduced LPS-induced expressions of iNOS and COX-2 and activation of MAP kinases in a dose-dependent manner. Among the fractions of the methanol extract, the chloroform and ethyl acetate fractions exhibited the most effective anti-inflammatory activities. These results show that the anti-inflammatory effects of TOLs are probably due to down-regulation of NO, $PGE_2$, and pro-inflammatory cytokines and reduced expressions of iNOS and COX-2 via inactivation of the MAP kinase signal pathway.