The present invention relates to microparticles comprising: at least one type of a platinum-based catalyst; and a thermoplastic polyolefin resin with a Z-average (Mz) of a weight average molecular weight (Mw) of at least 2500 and Mz/Mw of not more than 2.0, wherein the platinum-based catalyst is dispersed in the thermoplastic polyolefin resin. The microparticles make it possible to obtain a one-component curable organopolysiloxane composition having characteristics such as excellent storage stability.