Experimental and numerical studies were carried out on the natural convection of mercury in a rectangular container heated from a vertical wall. A magnetic field was applied parallel to the gravity vector and to the heated wall. Experimental results showed that the magnetic field decreased the Nusselt number considerably in the low region of the Grashof number. The effect of the parallel field was found to be less than that for a field normal to the gravity vector, but it is still not negligible. Numerical results on the Nusselt number were found to predict approximately the experimental ones. Calculated velocity profiles displayed noticeable changes due to the application of the magnetic field. A broad stagnation region was formed in the core of the container.