<p>Provided is a magnesium oxide powder that can be used as a filler for a resin composition in which high electrical insulating and heat conducting properties are desirable. The magnesium oxide powder contains, in terms of the number of particles, at least 30% of polygonal magnesium oxide particles which have BET equivalent particle diameters in the range of 0.5-20µm and which are cuboid bodies in which the vertex and/or one of the sides thereof has a chamfered shape.</p>
