Patient safety is an important healthcare issue worldwide, and patient accidents in the operating room can lead to serious problems. Accordingly, we investigated the explanatory ability of a modified theory of planned behavior to improve patient safety activities in the operating room. Questionnaires were distributed to perioperative nurses working in 12 large hospitals in Korea. The modified theory of planned behavior data from a total of 330 nurses were analyzed. The conceptual model was based on the theory of planned behavior data, with two additional organizational factors—job factors and safety management system. Individual factors included attitude, subjective norms, perceived behavioral control, behavioral intention, and patient safety management activities. Results indicated that job factors were negatively associated with perceived behavioral control. The patient safety management system was positively associated with attitude, subjective norm, and perceived behavioral control. Attitude, subjective norm, and perceived behavioral control were positively associated with behavioral intention. Behavioral intention was positively associated with patient safety management activities. The modified theory of planned behavior effectively explained patient safety management activities in the operating room. Both organizations and individuals are required to improve patient safety management activities.