Although segmental or subsegmental atelectasis may occur during anesthesia, mucous plugging of a mainstem bronchus has been uncommonly reported in anesthetized patients with chronic respiratory disease. However, pulmonary atelectasis following mucous plugging may rarely result normal patients. We report this case of an allegedly healthy patient was developed a left main stem bronchus obstruction, resulting in subsegmental collapse of left lower lung after the induction of general anesthesia.