Magnetization force caused by a magnetic field gradient (F-m) is a body force and can cause buoyancy. We numerically simulate the natural convection arising from the depletion of protein concentration around a growing protein crystal when an upward magnetization force acts on the solution, The numerical predictions reveal that an upward magnetization force can damp convection. When a magnetic field gradient mu H-2(0)(dH/dz) = -685 T-2/m is applied, the maximum flow velocity is reduced by about 50% and the velocity in the vicinity of the crystal is reduced by about 24%. Due to the low electric conductivity of the solution, the contribution of the Lorentz force is negligible. When mu H-2(0)(dH/dz) = -1370 T-2/m, the upward magnetization force (F-m approximate to pg) damps convection completely. Our study shows a new method of controlling convection in the process of protein crystal formation.