Weaning is the process of going from ventilator dependence to spontaneous breathing. Its complications can be avoided by nursing care. Aim: This study aimed to determine relationship between nurses' knowledge of evidence –based practice and patients' health outcomes as regards weaning patients from mechanical ventilation in the intensive care units at Elmahala and Benha Hospitals. Setting: the study was carried out at El-Mahalla chest hospital and Benha University hospital in the intensive care units. Subjects: All available nurses (40 nurses from El-Mahalla chest hospital and 40 from Benha University hospital) were included in the study. A purposive sample comprised 80 adult alert patients who were assigned for nurses caring them, 40 patients from El-Mahalla chest hospital and 40 from Benha. Tools were developed through reviewing of related recent literature. tool 1: A Structured questionnaire included two parts, part I: Socidemo-graphic characteristics for nurses and patients' interview Schedule. Part II: Nurses' Knowledge assessment. Tool 2: Nurses' practice observational checklist related to actual nursing care for weaning patients. Tool 3: Patients' Health Outcomes included, general and Respiratory assessment as ABGs, swallowing reflex, respiratory pattern, breathing sound as well as cough and secretion. Result and conclusion: The findings of the current study concluded that the nurse's knowledge as regards MV weaning was adequate and satisfactory by all nurses in Elmahala Hospital and the majority in Benha Hospital. On the other hand, the majority of studied nurses had unsatisfactory practice in both hospitals El-Mahalla and Benha. These findings may be attributed to that the nurses didn't integrate their knowledge into practice in providing adequate nursing care concerning weaning patients from MV. Concerning patients' health outcome, there were significant relations between patients' sleep, mental status, mobility, and breathing sounds and nurses' knowledge and practice in both hospitals. In addition, the nurses' practice in El-Mahalla hospital has a significant relation with the patients' respiratory and heart rates. Also, there was a significant relation between patients' swallowing reflex, respiratory pattern, and the nurses' knowledge in Benha. Recommendations: Further research should focus on developing and implementing strategies designed to decrease the incidence of extubation, weaning failure and complications based on their predictors.