Introduction : Therapeutic mannitol has shown beneficial effects on prognosis and mortality in traumatic brain injury patients, especially with improved intracranial pressure. Objectives : This study aims to investigate the relationship between mannitol administration and the distribution width of red blood cells in traumatic brain injury in Wistar rats. Methods : This research was conducted using a laboratory experimental method on mice with a post-test control group design. There were two treatment groups and one control group. The study was conducted at the Laboratory Animal Faculty, Medical University Hasanuddin, for a period of 14 days in the month of February 2024. The estimated sample size for this study was determined using the Federer formula. The minimum sample size for each group was 9 mice, making a total of 27 mice for the research. The analysis used was one-way ANOVA (analysis of variance) and the Post Hoc Test using the LSD method for parametric data