Background: Intensive care unit (ICU) is among the most important hospital wards. Variety of scoring systems for evaluation of patients' status and prediction of hospitalization outcomes in ICU has been raised that each has strong and weak points; assessment of these characteristics tends to promote new scoring systems. The current study compared scoring systems of Mortality Probability MODEL-III (MPM-III) and Simplified Acute Physiology Score-III (SAPS-III) in trauma patients in ICU. Methods: This randomized cross-sectional study was conducted on 200 patients admitted in ICU because of trauma in years 2016-17. Patients' information including demographics, mean of systolic, diastolic, and arterial blood pressure, pulse, respiratory rate, temperature, Glasgow coma scale (GCS), arterial gas analysis, white blood cell (WBC) counts, hematocrit, bilirubin, creatinine, type of admission, and presence of underlying diseases were extracted from records; MPM-III and SAPS-III were measured for these patients and compared. Findings: MPM-III scoring system had discrimination of 0. 935 [95% confidence interval (95%CI): 0. 89-0. 97; P < 0. 001) in cut-off point of 0. 13, and its sensitivity and specificity was 87% and 84%, respectively. For SAPS-III system, in cut-off point of 0. 13, the discrimination was 0. 77 (95%CI: 0. 69-0. 85; P < 0. 001), with the sensitivity of 80% and specificity of 68%. Based on both MPM-III and SAPS-III systems, mortality was in correlation with duration of ICU admission (P = 0. 001 for both systems) and duration of intubation (P < 0. 001 for both systems), while only for SAPS-III, total duration of hospitalization was in correlation with mortality (P < 0. 001). Conclusion: MPM-III scoring system was superior to SAPS-III regarding discrimination power in trauma patients. In addition, based on both systems, mortality rate was in direct association with days of ICU admission and intubation duration.