Background: Fluid balance is among important measures because it has a great importance in managing and understanding patients' clinical status recorded in patients' daily observation sheet. Monitoring fluid balance is a part of the scope of nurses' practice. Aim of the study: to evaluate the effect of educational protocol regarding accurate monitoring of fluid balance on critical care nurses' knowledge and practice.Research design: Quasi - experimental research design will be utilized to fulfill the purpose of this study. Setting: This study was carried out at six critical care units affiliated to Minia University Hospitals (Intensive care unit, renal intensive care unit, neurosurgical intensive care unit, cardiac intensive care unit, chest intensive care unit, stroke unit). Subjects: A Purposive sample of all critical care nurses who are working in six critical care units at Minia University Hospitals that mentioned before and willing to participate in the study was included. Tools of data collection: Two tools were designed and used for collecting data for this study, First Tool: structured questionnaire sheet, Second Tool: Nurses′ performance observational checklist sheet, Educational Protocol about accurate fluid monitoring. Results: There was a highly statistically significant difference in nurses' knowledge and practice pre and post educational protocol regarding monitoring fluid balance. Conclusion: results showed that there is a large wide gap between nurses′ knowledge and their practice regarding monitoring of fluid balance pre and post-educational protocol. Recommendations: Greater attention should be given for observing nurses' performance during monitoring fluid balance. Replication of the study should be done on a large probability sample