Disclosed are a polycrystalline MgO sintered compact, which has a sintered density close to the theoretical density, has good mechanical properties and thermal conductivity and can reduce the contamination of an atmosphere by gas evolution, and a process for producing the MgO sintered compact. The polycrystalline MgO sintered compact has such a unique crystal anisotropy that a large proportion of a (111) plane is aligned on a plane to which a uniaxial pressure has been applied. The polycrystalline MgO sintered compact is obtained by a process comprising the step of subjecting an MgO material powder having a particle diameter of not more than 1 [mu]m to uniaxial pressure sintering and the step of then performing heat treatment in an atmosphere having an oxygen content of not less than 0.05% by volume at a temperature of 1273 K or above for 1 min or longer.