Abstract. Forced convection uid ow and heat transfer were investigated in a porous channel with expanding or contracting walls, which was lled with Al2O3-Cu/water micropolar hybrid nano uid in the presence of magnetic eld. In order to solve the governing equations analytically, the least square method was employed. The hot bottom wall was cooled by the coolant uid, which was injected into the channel from the top wall. The range of nanoparticles volume fraction (90% Al 2 O 3 and 10% Cu by volume) was between 0% and 2%. The e ects of consequential parameters such as Reynolds number, Hartmann number, micro rotation factor, and nanoparticles volume fraction on velocity and temperature pro les were examined. The results show that with increasing Reynolds number, the values of temperature and micro rotation pro les decrease. Furthermore, when the hybrid nano uid is used, compared to common nano uid, the heat transfer coe cient will increase signi cantly. It is also observed that when the Hartmann number increases, Nusselt number increases, too.