This paper presents a numerical study of laminar forced convective flow of nanofluid-based water/Al2O3 in a two-dimensional horizontal microchannel heat sink. The governing equations are solved by using the finite volume method based on simple algorithm. The effect of solid nanoparticles on the heat transfer is investigated after comparing our results with experimental data. The founding results showed that the use of nanofluid has enhanced the heat transfer in comparison with pure fluid, and the increasing of Al2O3 concentration enhances the thermal and dynamic parameters. Nusselt number and friction coefficient have been enhanced with the increasing of Reynolds number. This work contributes to ameliorate the cooling systems by integrating the nanofluids in the next generation of microchannels heat sinks.