Background: Physical restraints are any devices or materials attached to patients' bodyprevent the patient from pulling the connected devices. Aim: assess factors affecting nurses' performance regarding use of physical restraint in critical care unit. Design:Descriptive exploratory designs were used. Setting: The study was conducted in Medical Intensive Care Unit at Ain Shams University Hospital, Egypt. Subjects: A convenient sample of 36 nurses was recruited from the previously mentioned setting. Tools: A structured interview questionnaire to assess nurses'demographic data and nurses' knowledge about physical restraint, use of physical restraint observational for assessing nurses' practice and questionnaire for assessing factors affecting nurses' performance regarding use of physical restraint. Results: Half of the studied nurse had satisfactory knowledge level. All the studied nurses had unsatisfactory level of practice. The majority of the studied nurses reported that the degree of experience is one of the most important factor affecting use of physical restraints properly,less than two third of the studied nurses reported that, separation of ICU patients' in a private room affects their ability to monitor the patients. No statistically significant relation between nurses' level of knowledge and their demographics data. Conclusion: most common factors affecting use of physical restraint is absence of clear policies to conduct physical restraint, no written consent for patient's approval on application of physical restraint and in addition to absence of continuous education about use of physical restraint. Recommendations: Developing hospital policy and procedure for physical restraints to be available for all nurses and physicians. A hospital consent policy for obligating doctor and nurses to get approval from patient or his / her family before application of physical restraint.