Background: Early mobilization among critically ill patients is a safe and effective intervention that can have a significant impact on functional outcomes and prevent immobility complications. Aim: This study aimed to assess nurses' perception regarding barriers of early mobilization among critically ill patients. Design: A descriptive exploratory design. Setting: Medical Intensive Care Unit at El-Demerdash hospital and the Cardiac Intensive Care Unit which affiliated to Ain Shams University Hospitals in Egypt. Sample: A convenience sample of 60 nurses working in the previous mentioned setting. Tools: 4 tools were used: Tool I: Nurses' Self-administered questionnaire. Tool II: Nurses' Practice Observation Checklist. Tool III: Nurses' attitude Likert Scale. Tool IV: Nurses' perception regarding barriers of early mobilization among critically ill patients. Results: revealed that, 63.3% of the studied nurses had unsatisfactory level of knowledge, 65% of them had un satisfactory level of practices, 58.3% of them had a negative attitude and 91.7% of the studied nurses agreed with ICU related barriers. 83.3% of the studied nurses agreed with nurses related barriers. Moreover, 60% of the studied nurses agreed with patient related barriers. Conclusion: More than two third of the studied nurses had unsatisfactory level of knowledge & practice. Also, majority of them agreed that ICU have highly barriers on early mobilization of critically ill patients. Moreover, more two third of nurses had negative attitude. In addition, there was highly significant correlation between total level of knowledge, attitude, barriers & practice regarding early mobilization among critically ill patients.  Recommendations: Attend training programs and workshops about early mobilization training to improve their knowledge and competency.