Numerical solution is carried out to analyze the effect of nanoencapsulated phase change material (NEPCM) slurry on forced convection heat transfer of steady laminar flow past an isothermal square cylinder. The base fluid is water while the NEPCM particles material is n-octadecane with an average diameter of 100 nm. A parametric study was performed for different volume fraction of nanoparticles ranging from 0% to 30%, two melting temperature ranges, i.e., 10 K and 20 K, and different inlet Reynolds numbers ranging from 15 to 45. The governing equations of flow and energy are solved simultaneously using a finite volume method (FVM) on collocated grid arrangement. It was found that for both NEPCM slurry and pure water, local and average heat transfer coefficients increases with increasing Reynolds number. The results of heat transfer characteristics of slurry flow over the square cylinder showed remarkable enhancement relative to that of the base fluid. The enhancement intensifies for higher particle volume concentrations and higher Reynolds numbers. However, utilizing the slurry can cause higher shear stress on the wall due to higher viscosity of mixture compared to the pure water. The melting temperature range of NEPCM particles has slight effect on heat transfer, although with increasing volume fraction and Reynolds number, lower melting range leads to higher heat transfer coefficient.