The Intensive Care Unit is a unique hospital setting, not only because of its physical environment but also because the patients are unstable and submitted to physical and psychological stresses. Delirium is a common disorder in Intensive Care Unit. It is still misdiagnosed by healthcare providers and is treated inappropriately or neglected. Nursing care for delirium includes regular assessment and monitor frequently for at risk patients. The present study aimed to evaluate the effect of educational program on nurses' knowledge, practice and clinical outcome regarding delirium among critically ill patients. The study was conducted at Intensive Care Unit at Tanta University Hospital. It included 40 critical care nurses working in the previously mentioned setting. Also, 40 critically ill patients were used in this study. They divided into two equal groups. 20 critically ill patients were evaluated before implementation of educational program. Another 20 critically ill patients were evaluated after implementation of educational program. Three tools were used in the study for data collection. Instrument 1 is a structure questionnaire sheet. It was divided into two parts; Part A: nurses' socio demographic assessment sheet. Part B: nurse's knowledge assessment sheet, Instrument 2: Observational Checklist and Tool 3: Intensive Care Delirium Screening Checklist (ICDSC). The main results of this study were that, the majority of the studied nurses have good knowledge after educational program. Also, the majority of studied nurses (97.5%) have poor score in their practice pre educational program compared to 77.5% % of them had good score in their practice post test. Also, about 30% of pre test group had delirium at 5th, 6th, and 7th days of admission compared with 10% in the post program group. The study recommended that In-services training program should be done continuously for updating critical care nurses' knowledge and practices regarding delirium detection and prevention. Also, Cognitive assessment in general and delirium assessment in particular should be incorporated into nursing education courses.