Achillea Wilhelmsii have been used in folk remedies. The relaxant effects of the extract of A. Wilhelmsii on tracheal chains of guinea pigs were examined. The relaxant effects of four cumulative concentrations of the extract, theophylline and saline were examined by their relaxant effects on precontracted tracheal chains of guinea pig by KCl (group 1), 10 mM methacholine (group 2), incubated tissues by atropine, propranolol and chlorpheniramine and contracted by KCl (group 3) and incubated tissues by propranolol and chlorpheniramine and contracted by methacholine (group 4). In group 1 and 2, all concentrations of theophylline and three higher concentrations (4, 6 and 8 mg/mL) of the extract showed significant relaxant effects compared to that of saline. In groups 3 and 4 experiments also all concentrations of the extract showed significant relaxant effects compared to that of saline. The relaxant effect of three higher concentrations (4, 6 and 8 mg/mL) of the extract in group 1 were significantly greater than those of group 2 and in group 3 were significantly lower than those of group 1. There were significant positive correlations between the relaxant effects and concentrations for theophylline in groups 1 and 2 and the extract in all four groups of experiments. These results showed a potent relaxant effect for the extract from A. Wilhelmsii on tracheal chains of guinea pigs. A muscarinc receptor blockade was also suggested for the extract.