Background: Nurse's performance remains long standing determinates of quality of care for patients, many factors affecting the performance of nurse in emergency operating rooms. Patient safety is a key component of nurses' performance. Nurses have an important role for maintaining patient safety. The aim of the study was to assess factors affecting nurses ' performance regarding patient safety in emergency operating rooms. Research design: A descriptive design was carried. Setting: This study was conducted at the operating rooms in emergency and new surgery hospitals at Zagazig University, Egypt, a convenience sample of all available nurses (70). The tools of data collection: An Interview questionnaire about personal characteristics of studied nurses, nurses' knowledge and factors affecting nurses' performance, an observational checklist to assess nurses` practices. The results revealed that, 52.9% of studied nurses had unsatisfactory total knowledge. 38.6% of studied nurses had unsatisfactory total practice. In relation to factors, 91.4% of studied nurses had affected by planning and coordination, 88.6% by equipment, 84.3% by communication and 80% by procedures. The majority of studied nurses' performance regarding patient safety (80%) had affected by total factors. The study finding concluded that, there was a positive significant correlation between total knowledge, total practice and factors affecting nurses` performance. Recommendation: Training programs for all operating room nurses’s to improve their knowledge and practice regarding patient safety. Factors affecting nurses' performance should be evaluated by the nursing management and hospital administration to avoid or correct such factors.