Objective: To explore the effect of 21-aminosteroid (U-74389G) on brain edema post traumatic brain injury (TBI) in rats. Methods: Water content of brain after TBI was assayed by means of dry/wet weight methodology, and the content of ion was measured by an atom absorption spectrum analysis apparatus. Results: The turbulence of sodium, potassium, calcium and magnesium after TBI could be alleviated by U-74389G. The increased water content of injured brain tissue could also be alleviated by the administration of U-74389G. Conclusion: The study indicates that U-74389G could effectively improve brain edema after TBI