PURPOSE: The titled composite, obtained by impregnating a metallic oxide prepared by the thermal decomposition of a metallic hydroxide with an alkoxysilane compound, and having the suppressed hyrolysis of the alkoxyl groups.

CONSTITUTION: Particles of a metallic oxide obtained by the thermal decomposition of a metallic hydroxide are impregnated with an alkoxysilane compound expressed by the formula R-Si(OR')nY3-n (n is 1W3) to adsorb the alkoxysilane compound on the surfaces thereof. Particles of aluminum oxide obtained by the thermal decomposition of aluminum hydroxide are used as the particles of the metallic oxide. The resultant alkoxysilane composite is then mixed with a rubber or plastic to give a crosslinkable composition.