The effect of applying a static magnetic field on mass transfer rate in diffusion-controlled electroreduction was studied experimentally around single spheres of diameters 8 to 14 mm under the condition of laminar natural convection. The electrolytic solution of the system K3Fe(CN)(6)K4Fe(CN)(6) with a supporting electrolyte was employed and the magnetic field was applied to the cathode in the horizontal or vertical direction and up to 336 mT in flux density. By applying the magnetic field in every direction, the mass transfer rate was enhanced more than 50 % at the highest magnetic flux density, compared to the simple natural convection case. From the obtained data of mass transfer coefficients, dimensionless regression equations for each direction of the applied magnetic field were derived where the magneto-diffusion factor was introduced so as to express the contribution of the applied magnetic flux density.