Background: Blunt abdominal trauma (BAT) has a high rate of morbidity and mortality. In the past few years, focused assessment with sonography in trauma (FAST) and computerized tomography (CT) scan have been extensively utilized and studied in management of BAT. The present study aims to compare the diagnostic accuracy of FAST and CT scan in detection of free fluid in BAT patients. Methods: In this cross-sectional study, patients with BAT were evaluated by both FAST and CT scans in Shahid Sadoughi Hospital, Yazd, Iran, from May 2017 to February 2018. The results were compared and the sensitivity, specificity, and accuracy of FAST and CT scan were calculated. In addition, the accuracy of FASTs performed by emergency medicine residents (EMR) was compared with those procedures performed by radiology residents (RR) in detecting abdominal free fluid following blunt trauma. Results: In this study, 175 patients were participated and most of them were males. The commonest cause of trauma was a road traffic accident (RTA). When FAST was performed by EMRs, sensitivity was  96.3%, specificity 75%, 60% positive  and 98.1% negative predictive values and 94.8% accuracy in true evaluating free fluid , and Sensitivity 97.5%, specificity 83.3%, 71.4%  positive and 98.8%  negative predictive values  when FAST was performed by RRs. Conclusion: Based on this study finding, it seems that FAST is highly sensitive, specific and accurate in the initial evaluation of patients with BAT.