There are provided a novel polymerizable composition having an X-ray contrast property and excellent transparency, a cured product thereof, and a composite material comprising powder of the cured product. More specifically, there are provided a polymerizable composition comprising (A) an inorganic oxide having an X-ray contrast property and an average particle diameter of 100 nm or smaller, (B) a surface modifier, (C) a polymerizable compound and (D) a polymerization initiator, a cured product obtained by polymerizing these components, and a composite material comprising powder of the cured product.