Objective:The risk of methicillin-resistant Staphylococcus aureus infections in Intensive Care Unit (ICU) is increasing in recent years with high rate of morbidity and mortality. Therefore, in this study, we aimed to evaluate the rationale use of vancomycin in ICU patients.Methods:A total of 200 patients who received at least 48 h intravenous vancomycin were randomly selected from ICU wards, during 9 months. Vancomycin administration and related clinical and laboratory data were gathered from patients' charts and health information system to evaluate the appropriateness of different aspects of vancomycin use during all days which vancomycin were ordered.Findings:During the study, 15,230 ± 1216 mg (mean ± standard error of the mean [SEM]) vancomycin was administered for 200 patients in the mean period of 9.79 ± 0.64 (SEM) days of ICU stay, for prophylaxis and empiric therapy. Results showed the appropriateness of vancomycin uses were 30.5%, 9%, and 5.5% in the first 24 h, after 72 h and during the whole time of treatment, respectively. In addition, infectious consultation was the only significantly different parameter between appropriate and inappropriate vancomycin administration groups (P < 0.001).Conclusion:Although vancomycin utilization evaluation were mentioned in previous studies, but data related to ICU patients and during all days of vancomycin therapy are limited. High prevalence of inappropriate use of vancomycin in ICU is alarming for health systems and necessitates implementation of antibiotic policies.