Four surgical operations were going on in our hospital when the 9.0-magnitude earthquake hit northeast Japan on March 11, 2011. To work out effective disaster prevention measures, we investigated how did nurses in the operating room acted immediately after the earthquake, and their psychological state. We distributed questionnaires to 17 nurses who had been in the operating room at that time. Our study showed that most nurses formed cool judgments on the safety and helped allay the anxiety of the patients, despite the fact that they themselves felt anxiety or were terrified at heart. On the other hand, several actions such as the protection from contamination of the operative field were not taken properly as prescribed in the Emergency Manual of the operating room. Full awareness of role-sharing flowcharts of emergency evacuation of the patient under operation, and periodical disaster drills are needed to plan for a crisis.