Background: Heavy workload is one of the main problems of nurses working in intensive care units (ICUs). It not only decreases the quality and safety of patient care, but also increases human errors in health care, rate of hospitalization, and risk of mortality in patients. Workload evaluation and surveillance of patients enable authorities to allocate adequate staff to ICUs, leading to improved quality of patient care and treatment. Objectives: The present study aimed to evaluate nurses’ workload and efficiency of nursing staff allocation in a trauma ICU of Shahid Rajaee hospital, affiliated to Shiraz University of Medical Sciences. Methods: In this cross sectional study, we evaluated nurses’ workload in a trauma ICU. The evaluation was based on the nursing activities score (NAS) system and was performed in the morning, evening, and night shifts for 1 month. In this period, all nursing care activities provided for 36 patients in this unit were monitored and recorded. Additionally, the number of nurses required per shift was estimated, based on the required and available time for care. Efficiency of nursing staff allocation was evaluated accordingly. Results: The mean age of the patients was 40.17 ± 22.30 years, and the length of ICU stay was 9.79 days on average. Based on the findings, the mean NAS score was 65.3 ± 23.19%. Moreover, the number of nurses in the morning and evening shifts was less than the required number, except for days 3 and 7. On the other hand, the number of nurses in the night shifts was proportional to the required number. Conclusions: The results indicated a heavy nursing workload in the ICU. Our findings also suggest that the quality of patient care can be improved by balanced distribution of workforce relative to workload in different shifts.