The natural convection of liquid metal in a cubical enclosure was numerically studied for various electro-conductivities of the wall from zero to infinity under a static magnetic field. The cubical enclosure was heated from one vertical wall and cooled from an opposing vertical wall both isothermally and four other walls were thermally insulated. The direction of the static magnetic field was perpendicular to the heated and cooled walls (X-direction) or parallel to the heated and cooled walls (Y-direction) for the present work. All calculations were carried out for the Rayleigh number 10(5), the Prandtl number 0.025, and the Hartmann number 100. Under the X-directional magnetic field, the average heat transfer rate was effectively suppressed with an increase in the electro-conductivity of the wall. Under the II-directional magnetic held, the average heat transfer rate was only slightly suppressed for the electrically insulated wall, but drastically decreased with an increase in the electro-conductivity of the wall.