The aim of this study was to identify major anti-inflammatory compounds in Alopecurus aequalis Sobol. (A. aequalis). The ethanol extract and the hexane-, dichloromethane-, ethyl acetate- and n-butanol-soluble fractions derived from A. aequalis were evaluated in order to determine their inhibitory effects on nitric oxide (NO) production in RAW 264.7 cells stimulated with lipopolysaccharide (LPS). The ethanol extract decreased NO production in a dose-dependent manner without any evidence of cytotoxicity at a concentration range of 0-200 µg/ml. The ethyl acetate soluble fraction was the most potent among the four soluble fractions. A compound was isolated by reversed-phase high-performance liquid chromatography from the ethyl acetate soluble fraction and this was identified to be tricin. Tricin inhibited the LPS-induced NO production in a dose-dependent manner without any evidence of cytotoxity at a concentration range of 1-100 µg/ml. Tricin also inhibited the LPS-induced production of prostaglandin E2. Western blot analysis indicated that tricin decreased the LPS-induced increase in the protein levels of inducible NO synthase and cyclooxygenase. In addition, tricin suppressed the production of intracellular reactive oxygen species in the LPS-stimulated RAW 264.7 cells, as measured by flow cytometry. Taken together, our results clearly indicate that tricin is a major functional anti-inflammatory compound which can be isolated from A. aequalis extracts.