Purpose: This study developed an in-service training program for patient safety and aimed to evaluate the impact of the program on nurses in the operating room (OR). Methods: A pretest–posttest self-controlled survey was conducted on OR nurses from May 6 to June 14, 2020. An in-service training program for patient safety was developed on the basis of the knowledge–attitude–practice (KAP) theory through various teaching methods. The levels of safety attitude, cognition, and attitudes toward the adverse event reporting of nurses were compared to evaluate the effect of the program. Nurses who attended the training were surveyed one week before the training (pretest) and two weeks after the training (posttest). Results: A total of 84 nurses participated in the study. After the training, the scores of safety attitude, cognition, and attitudes toward adverse event reporting of nurses showed a significant increase relative to the scores before the training (p < .001). The effects of safety training on the total score and the dimensions of safety attitude, cognition, and attitudes toward nurses’ adverse event reporting were above the moderate level. Conclusion: The proposed patient safety training program based on KAP theory improves the safety attitude of OR nurses. Further studies are required to develop an interprofessional patient safety training program. In addition to strength training, hospital managers need to focus on the aspects of workflow, management system, department culture, and other means to promote safety culture.