The present invention relates to composite particles, coated particles, a method of producing composite particles, a ligand-containing solid phase carrier, and a method of detecting or separating a target substance in a sample. The above described composite particles each contains an organic polymer and inorganic nanoparticles, wherein the content of the inorganic nanoparticles in the composite particles is more than 80% by mass, and wherein the composite particles have a volume average particle size of from 10 to 1,000 nm.