In this paper, the effects of thermal radiation and magnetic field on the fluid flow and heat transfer of the nanofluids in a square cavity are numerically studied. The square cavity is filled with the absorbing-emitting-scatterng Al₂O₃/water nanofluids, which is assumed to be viscous, incompressible, and also have electrical conductivity. The top and the bottom walls of the square cavity are perfectly insulated while the left and right vertical walls are maintained isothermal. All the governing equations are solved by using the collocation spectral method. After the validation of numerical results, streamlines, isotherms, and Nusselt number are analyzed for the effects of the inclination angle of the magnetic field and the emissivity of walls.