Background: Urine color (UC) is affected by fluid intake and loss from the body. Critically ill patients are exposed to many stressors added to the fluid intake or loss that can disturb body fluids movement affecting the color of the excreted urine. Aim: To assess factors affecting change of the urine color as a hydration indicator among critically ill patients. Design:  A descriptive research design was used. Setting: The study was conducted at three general intensive care units in the Teaching Main University Hospital, Alexandria, Egypt. Subjects: A purposive sample of 150 critically ill adult patients having a urinary catheter on the first day of admission to the selected setting. Tools of data collection: (1) Patient's demographic and clinical data assessment (2) Urine color chart. Results: 70.5% of the studied patients showed UC of dehydration. UC changed insignificantly with the unconscious state (P = 0.73) and changed significantly with age over 40 years, increased body temperature, diagnosis of respiratory and neurological alteration, general edema, mechanical ventilator, blood urea nitrogen and blood osmolality (P ≤ 0.05). Conclusions: Some factors specific to critically ill patients can affect UC significantly such as age, temperature, diagnosis, mechanical ventilator, edema, blood urea nitrogen and blood osmolality. Recommendations: critical care nurses should not depend on change of the UC alone for confirming dehydration in critically ill patients.