Hydrocyclones are devices used to treat produced water in the petroleum industry. These gadgets are employed especially at offshore fields, due to restrictions of charge and space. Several factors may affect the performance of the oil/water separation by hydrocyclones. Among these factors are the geometry and processing capacity of the hydrocyclones, oil droplet size, density difference between the phases, pressure drops, and temperature fluctuation. This paper aims to analyze the effects of inlet fluid mixture temperature and oil droplet size on hydrocyclone performance in separating dispersed heavy oil from continuous streams of water. The experiment used a commercial package, ANSYS CFX 11. Numerical results clearly indicate that superficial velocity and oil mass flow rate in the overflow have a positive relationship with oil droplet size and temperature. The pressure drop decreased from 155.857 to 141.966kPa and the separation efficiency changed from 58.97 to 60.11% when the inlet temperature increased from 20 to 100°C using a 40μm oil droplet diameter.