Acicular or platy titanium suboxides, expressed by the general formula, TiOx where x is a positive real number less than 2, have a geometric anisotropy as an aspect ratio in the acicular or platy form of 3 or more, a higher specific surface area and a greater geometric anisotropy even in comparison on the basis of the same degree of reduction, and are capable of retaining their native configurations during the reduction. The resin mediums incorporated with the acicular or platy titanium suboxides have good electric properties, and a higher mechanical strength.