Abstract : In the present paper, the three-dimensional Computational Fluid Dynamics (CFD) simulation of heat transfer and fluid flow in two types of heat sinks are presented. The plate fin and circular pin fin heat sinks are simulated for different air velocity inlet. Thermal and hydraulic performances of plate fin and circular pin fin heat sinks are obtained. Numerical predictions of thermal resistance and pressure drop in the heat sinks are compared with experimental results from the literature and an excellent agreement is found. The results also show that the circular pin fin heat sink has better performance than the plate fin heat sink. For the plate fin heat sink, the thermal resistance varied from 2.92 oC/W to 0.99 oC/W, whereas the pin fin heat sink varied from 2.69 oC/W to 0.89 oC/W.