Artemisia iwayomogi has been used in Korea for many centuries as a treatment for anemia. The effect of Artemisia iwayomogi on tracheal smooth muscle is not known. The purpose of the present study is to determine the effect of Artemisia iwayomogi on histamine induced tracheal smooth muscle contraction in guinea pigs. Guinea pigs(500g, male) were killed by CO₂ exposure and a segment (8-10mm) of the thoracic trachea from each rat and guinea pig was cut into equal segments and mounted ‘in pairs’ in a tissue bath. Contractile force was measured with force displacement transducers under 0.5g loading tension. The dose of histamine (His) which evoked 50% of maximal response (ED₅₀) was obtained from cumulative dose response curves for histamine (10^-7～10^-4M). Contractions evoked by His (ED₅₀) were inhibited significantly by Artemisia iwayomogi. In guinea pig tracheal smooth muscle, the mean percent inhibition of histamine induced contraction was 31.9% (p<0.05) after 100㎕/㎖ Artemisia iwayomogi. L-NNA slightly but significantly attenuated the inhibitory effects of Artemisia iwayomogi. Following treatment with L-NNA, the mean percent inhibition caused by 100㎕/㎖ Artemisia iwayomogi fell to 44.6% in guinea pig induced by histamine contraction. Propranolol, indomethacin and methylene blue did not significantly alter the inhibitory effect of Artemisia iwayomogi. These results indicate that Artemisia iwayomogi can relax histamine induced contraction of guinea pig, and that this inhibition related to nitric oxide formation.