Vasovagal syncope accounts for the majority of adverse events that occur in dental offices and is normally related to emotional or somatic factors. The factors trigger intense parasympathetic state, leading to bradycardia and hypotension. We experienced a case of vasovagal syncope just before general anesthesia. A 49-year-old woman with alveolar bone deficiency on maxilla and mandible was planned to undergo an alveolar bone graft with mandibular body under general anesthesia. She didn't have any histories of disease, medication or syncope. Though she showed a little anxiety from admission, she had no pre-operative medication. After she was guided to the operating room, she had signs and symptoms of vasovagal syncope without any prodromes. The patient was resuscitated soon only by the conservative treatment and was operated under general anesthesia.