The present study investigates heat transfer of nanofluid flow in micro channel heat sink (MCHS) in the presence of a magnetic field. Al2O3-water nanofluid is chosen the best among other nanolfluid and is used as a coolant fluid in solution. The KKL correlation is utilized for calculation of the effective thermal conductivity and viscosity of nanofluid. Modified Darcy equation is applied for porous medium and the two-equation model with thermal dispersion is employed for heat transfer between fluid and solid sections. Since the coupled heat transfer equations of nanofluid and solid phase are nonlinear, the analytical Collocation method (CM) is employed to solve this problem. Effects of the Hartmann number, nanoparticles volume fraction, nanoparticle diameter, porosity, channel aspect ratio on temperature distribution, velocity and Nusselt number are investigated deliberately. Results show that Nusselt number has direct relationship with applying a magnetic field on MCHS. (C) 2017 Elsevier B.V. All rights reserved.