Abstract: A microparticle catalyst for hydrosilylation reactions which contains microparticles of an average particle diameter of 0.1 to 20 .mu.m made of a metallic catalyst for hydrosilylation reactions; a disiloxane having the general formula (R.sup.1 R.sup.2 ArSi).sub.2 O, wherein, R.sup.1 is an alkenyl group, R.sup.2 is a monovalent hydrocarbon group and Ar is an aryl group; and a resin having a glass transition temperature of 40.degree. to 200.degree. C. and thermosetting silicone composition containing the microparticle catalyst.