This study was designed to investigate whether a methanol extract of chlorella can suppress oxidative stress and nuclear factor kB (NFkB) activation in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophage cells. Treatment of RAW 264.7 cells with chlorella methanol extract (25, 50, and 100 $mu$g/mL) significantly reduced LPS-stimulated nitric oxide production in a dose-dependent manner. Treatments with chlorella methanol extract at all concentrations also reduced thiobarbituric acid-reactive substances accumulation and enhanced glutathione level at 50 and 100 $mu$g/mL levels. The specific DNA binding activities of NFkB on nuclear extracts in cells treated with 50 $mu$g/mL and 100 $mu$g/mL chlorella methanol extracts were significantly suppressed. These results suggest that chlorella methanol extract has mild antioxidative activity and the ability to suppress intracellular oxidative stress and NFkB activation.