Background: Fluid and electrolyte balance are critical for the maintenance of life and homeostasis. Therefore, the aim of this study was to evaluate nurses' knowledge and practice in maintaining fluid and electrolyte balance. Methods: Quasiexperimental design [pre, post, and follow-up tests] was utilized to fulfill the purpose of the study. Settings: This study was conducted at Pediatric Intensive Care Units, Menoufia Governorate, Egypt. Sample: A convenient sample of fifty nurses was represented in this study from January to August 2021. Two tools were used for collecting data. First tool: Fluid balance monitoring questionnaire consisted of two parts to assess nurses' knowledge regarding fluid and electrolyte balance and the second tool: Fluid balance monitoring audit to assess nurses' practice of fluid balance monitoring. Results: The mean age and standard deviations of studied nurses were 28±6.9 and 34% of them were aged between 25 and 30 years old. Half of the study sample [50%] had a bachelor's degree. On the pre-test, there were moderately adequate knowledge and incompetent practices of fluid balance monitoring. In conclusion: The study revealed that implementation of a health education program has a positive outcome on the advance of nurses' knowledge and practices about fluid measurement and maintenance. Recommendation: Ongoing in-service education programs must be implemented at Intensive Care Units in order to boost nurses' knowledge, practice, and outcome.