Efforts from various approaches have been made to anesthetize myasthenic patients associated with thymoma and, on a ehoice of kinds and dosage of the muscle relaxants, there were considerable solicitude of the anesthesiologist. In recent years, intermediate aeting none depolarizing muscle relaxants were developed and its use tends to increase. we used with the divided dose administration of small amount vecuronium and observed the degree of relaxation using peripheral nerve stimulator for endotracheal intubation and maintenance of anesthesia. On the basis of our experience, we would like to recommand techniques that administrate the divided dose of small amount vecuronium as a musde relaxant and use peripheral nerve stimulator during general anesthesia.