Background: Mechanically ventilated patients suffer from serious complications. Implementing ABCDE bundle has positive impact on patients' outcomes. Intensive care unit nurses must be aware about all the component of the bundle and how to implement it in a correct way. Aim: the current study aimed to assess nurses' performance regarding ABCDE bundle for mechanically ventilated patients at the intensive care unit Research design: A descriptive exploratory design was utilized to conduct this study. Setting: This study was conducted at the adult intensive care unit Cardio-thoracic hospital affiliated to Sednaoui hospital. Type of the sample: A convenient sample of (70) nurses and a purposive sample of mechanically ventilated patients(80) were included in the study Four tools were used: Tool І: A structured interview questionnaire Tool II: Nurses' practices observational checklist Tool ІІІ: Sedation Scale of Richmond-Agitation Tool ІV: Confusion Assessment Method for the ICU Result: reveals that only 7.1% of the studied nurses had satisfactory level of knowledge regarding ABCDE bundle and delirium and its management, also, only 13% of the studied nurses had total competent level of practices. The study illustrated that 36.3% of the studied patients had sever delirium, while, 30.0% of them mild or moderate delirium. Finally, there were statistically significant negative correlations between total delirium scores of the studied patients and knowledge and practices scores of the studied nurses. More than two thirds of the studied nurses didn’t attend any training programs regarding ABCDE bundle. Conclusion: The majority of studied nurses to all of them had unsatisfactory knowledge regarding ABCDE bundle and delirium and its management and more than four fifths of them had total incompetent practices scores regarding ABCDE bundle implementation, more than one third of the studied patients had sever delirium, while, about one third of them mild or moderate delirium. Recommendations: The hospital should encourage cooperation among health care members regarding implementation of ABCDE bundle for better results.