Dimethyldichlorosilane is selectively and efficiently prepared by reacting methyl chloride with a solid contact mass comprising silicon and a catalytically effective amount of copper or a copper compound, said copper catalyst comprising (i) from about 10 to 1000 ppm of tin, antimony, or admixture thereof, or of a tin or antimony compound, or admixture thereof, (ii) from about 0.01 to 2% by weight of at least one of the metallic additives barium and strontium, or compound thereof, and, optionally, (iii) from about 0.01 to 3% by weight of zinc or a zinc compound.