Heavy crude oils contain considerable amounts of contaminants (e.g., sulfur, nitrogen, and heavy metals) and asphaltenes. The high contents of such contaminants in crude oil would decrease the efficiency of the refining process at the distillation column and lead to various problems such as air pollution, corrosion, and catalyst poisoning. Viewing such difficulties, the objective of this paper is to study the effect and performance of the hydrotreating process of heavy crude oil before atmospheric distillation. Such a process is expected to improve the properties of heavy crude oil and consequently increase the efficiency of the refining process. Process simulation of such process was performed via ASPEN HYSYS V.9., based on an existing Egyptian refinery plant with a feedstock of (50/50% mixture of light and heavy Arabian crudes). The process simulation results showed that a significant improvement had been achieved in the characteristics of crude oil after the hydrotreating process (e.g., lower contaminants content, lower density, and higher yield of middle distillates).