Qian Hu is the roots of Peucedanum praeruptorum Dunn. The object of the present paper was to determine the effects of water extract (QH-I) and petroleum ether extract (QH-M) of Qian Hu on smooth muscle contractility of isolated rabbit pulmonary artery rings. QH-I and QH-M antagonized pulmonary artery rings conlraction elicited by NE as well as KCl.QH-I and QH-M caused relaxation of rabbit pulmonary artery rings precontracted with NE as well as KCl. The contraction dose-response curves of pulmonary artery rings with NE were shifted to the right and the maximal contraction response were inhibited 73.1 ?8.0% and 43 .6? 4.2% by 1 .6 ? 10-5% and 8.0 ? 10-5%, QH-M, pD'2 = 4.72 ?0.43. These results indicate that Qian Hu may relax pulmonary artery smooth muscle directly as a Ca2+ antagonist