BACKGROUND: Vecuronium and Pancuronium have been proven to be associated with nicotinic receptor of skeletal muscle. Generally, nondepolarizing muscle relaxant is associated with contraction of smooth tracheal muscle, but there have been few studies about effects of nondepolarizing muscle relaxant on the smooth tracheal muscle. METHODS: We studied the acetylcholine dose response curve of the tracheal smooth muscle contraction and effects of propranolol, L-NAME after pretreating with vecuronium and pancuronium. RESULTS: Vecuronium shifted the acetylcholine dose-response curve of the tracheal contraction to the left, and pancuronium shifted the curve to the right. Vecuronium and Pancuronium reduced the contraction of smooth tracheal muscle with the use carbachol. Propranolol and L-NAME had no effect on the contraction of smooth tracheal muscle after pretreating with vecuronium and pancuronium. CONCLUSION: We suggest that vecuronium has an anticholinergic effect, while pancuronium has some effect on the muscarinic receptor in addition to its anticholinergic effect.