Natural convection in a laterally heated cross-shaped cavity is studied numerically. The flow structure and heat transfer are analyzed in a magnetic field at different Hartmann numbers (Ha) and Rayleigh numbers (Ra) determined from the temperature difference of the hot and cold walls. The magnetic field is illustrated to suppress convection, avoid instability, and control the heat transfer in the enclosure. Computational analysis is also performed to investigate the effect of the direction − horizontal or vertical − of the magnetic field and Prandtl number on the flow and temperature fields.