Isolated masseter spasm after succinylcholine administration is a rare abnormal response, but has been reported by a number of authors and is considered and early manifestation of malignant hyperpyrexia. We experienced a isolated masseter spasm after a small dose of succinylcholine administration in a facial palsy patient of central type due to brain tumor. It was likely that the intensity of this spasm was dose dependent to the amount of succinylcholine administration, and the spasm was prevented by pretreatment of nondepolarizing muscle relaxant. Anesthesia was performed safely for about 5 hours with nitrous oxide and halothane. We considered that this spasm was due to supersensitivity appearing at the denervated muscle.