Background: Aim of the study was to assess the nurses' performance regarding fluid, electrolytes and acid base imbalances for pediatrics and neonates. Research design: A descriptive research design was used. Setting this study was carried out in the paediatric and neonate intensive care at Assuit university paediatric hospital .Study sample consisted of all available nursing staff (130) nurses above mentioned setting.Tools were utilized for data collection: First tool nurses knowledge assessment tool, Second tool Nurses practice assessment tool. Results: The result of this study found that the majority of studied nurses were at the age group of 25 to < 30, females, married, and 58.5% were secondary school of nursing. Nearly half (47.7%) of studied nurses were having poor level of knowledge regarding fluid, electrolytes and acid base imbalances, and more than half(69.2%) of studied nurses have good level of performance, there were statistically significant difference between knowledge and practice of studied nurses regarding fluid, electrolytes and acid base imbalances. Conclusion: The general score of nurse poor level of knowledge and good level of practice regarding fluid, electrolytes, and acid base imbalances. Recommendations Provide in-service training programs for nurses to improve their performance regarding fluid, electrolytes and acid base imbalances. Key words: Performance, Fluid, Electrolytes, Acid Base & Imbalances.