Background: Dehydration is a serious public health concern occurred due to the imbalance between water intake and loss which increased in the climate change and Egypt's hot weather, lead to the morbidity and mortality rate raise among the older persons. Aim: To evaluate the effect of nursing educational program for improving older persons' hydration status. Subjects and Method: One group pre-post intervention research design. Setting: The study conducted at the (internal medicine and urology) clinics at the Assuit University hospitals. Sample: Total number of 130 older persons was included. Study tools: Contained four tools; Tool (I): Consisted of four parts; personal data, El-Gilany scale for measurement of socioeconomic status, health condition and knowledge of older persons regarding dehydration. Tool (II): Dehydration screening. Tool (III): Hydration knowledge scale and Tool (IV): Hydration facilitators and barriers attitude. Results: Mean ± SD and (range) of participant age: 69.28±7.65 (60-91). It was found that, more than half (56.9% &53.1% respectively) of them were male and had very low socioeconomic status. There was statistically significant effect of the educational program on the older persons' dehydration status; also there was improvement of older person's hydration & dehydration knowledge and attitude of older persons about hydration facilitators and barriers after the application of the educational program. Conclusion and recommendations: These results support that the nursing educational program improved the hydration status, hydration & dehydration knowledge and attitude toward hydration facilitators and barriers among older persons. Continuous educational programs about hydration status of older persons are recommended.