Background: Fluid balance monitoring is part of a nurse's scope of practice. Because fluid balance was calculated incorrectly, every patient management decision was influenced by incorrect fluid balance information. Aim: assess the effect of hybrid educational program on nurses' performance regarding caring of patients with fluid and electrolytes imbalance in Critical Care Units. Design: A quazi experimental design. Setting: The study was conducted at the critical care units at El Hussein university hospitals. Subjects: A purposive sample of (35) nurses. Data collection tools: Nurses' structured self- administered questionnaire and nurses' practices observational checklist. Results: the present study revealed that, more than half of the nurses had got unsatisfactory level of performance (knowledge & practice) regarding care of patients with fluid and electrolytes imbalance in critical care units at pre hybrid educational program implementation (57.10% and 54.30% respectively). Meanwhile, the majority of the study sample had got statistically significant improvement in their knowledge and practices regarding care of patients with fluid and electrolytes imbalance in critical care units at post hybrid educational program implementation (94.30% and 91.40% respectively). While this improvement lowered slightly post 3 months at follow up. Conclusion this study concluded that the hybrid educational program implementation for nurses‟ in the critical care unit was effective in improving their level of knowledge and practices regarding care of patients with fluid and electrolytes imbalance. Recommendations: Continuous evaluation of nurses‟ knowledge and practice is essential to identify their needs while caring for patients with fluid and electrolytes imbalance.