Abstract: OBJECTIVE To compare the effect of different extracts of Petasites japonicus on the contraction of isolated ileum of guinea pig. METHODS By using isolated guinea pig ileum experiments, histamine, acetylcholine load model were used as research models. Petasites japonicus was extracted by supercritical CO₂ and 80% ethanol respectively. The 80% ethanol extract was fracted by petroleum, ethyl acetate, n-butyl alcohol. The ethyl acetate extract was purified by silica gel column chromatography. Inhibition ratio of the contraction extent was calculated. RESULTS Different extracts of Petasites japonicus remarkably inhibited the contraction caused by histamine and acetylcholine. Ethyl acetate extract which was purified by silica gel column chromatography had the strongest inhibitory effect. CONCLUSION The different extracts of Petasites japonicus significantly inhibited the contraction of isolated ileum of guinea pig caused by histamine and acetylcholine. The effect of Petasites japonicus on the contraction of isolated ileum of guinea pig was fat-soluble components and was highly relevant to M ACh-receptors and H₁ receptors.