Two flavonoids (1 and 2) and one phenolic acid (3) obtained from Erigeron annuus have recently been shown to have potent antioxidant activities. Aim of this study was to investigate the inhibitory effects of these components on $interferon-{gamma}$ and lipopolysaccharide-induced nitric oxide productions in the mouse pheritoneal macrophage. Compounds 2 and 3 showed marked inhibitory activities against inducible nitric oxide synthase (iNOS) on the lipopolysaccharide and $interferon-{gamma}-stimulated$ mouse pheritoneal macrophages without cytotoxicity. Therefore, these results suggest that the compounds could be effective anti-inflammatory agents as nitric oxide inhibitors in vivo.