Background: The medical errors that caused death within 48 hours of the error involved insulin therapy. commonly to maintain the safety of critically ill patient, nurses are trained to care and be equipped with knowledge, skills and attitude to be the instrument of care. Aim: The purpose of this study was to assess nurses, knowledge, skill and attitudes toward insulin error for diabetic critical ill patient. Setting: This study was conducted in three of the ICUs of Assiut University Hospital. Sample: Eighty critical care nurses, working in the above mentioned settings, who apply insulin therapy administration, were recruited sequentially in this study. Eighty patients who were needed to insulin therapy and assigned to the observed nurses were included in this study. Tools: Three tools were used to collect the required data; nurses’ insulin therapy performance checklist, nurses 'structured questionnaire sheet for assessment of nurse's knowledge and nurses, attitude related to insulin errors. Results: Ten (12.5%) nurses’ have satisfactory performance and 70 (87.5%) of them have unsatisfactory. Concerning their knowledge, it is found that 20 (25%) of nurses had satisfactory knowledge, while 60 (75%) of them had unsatisfactory knowledge. most of studied nurses 25 (31.25%) had making ـ247 procedural errors, while 10(12.5%) demonstrated wrong route and charting errors. Positive attitudes also found toward the nurse workload become excessive, her performance is impaired (68.75%)and fatigue impairs performance during emergency situations (82.5%) . Negative attitudes were found toward documentation insulin therapy errors decrease punishment (42.45%). negative attitudes were reflected in disbelief that insulin assignment systems reduce insulin errors (43.75%). are in need for improvement. Conclusion: It was observed that the relationship between nurses' performance and their years of experience about insulin therapy there is statistically significant relationship between nurse's performance and their years of experience (F=4.045, P=0.024). Keywords: Nurse; knowledge; skill; attitudes; insulin errors; diabetic ill patients; critical care unit