A process for producing polymer particles having an antigen or an antibody introduced into the surface thereof, by carrying out miniemulsion polymerization using a monomer, a radical polymerization initiator, an emulsifier, and a hydrophobe in the presence of the antigen or antibody to thereby produce the polymer particles, is disclosed. According to the process, it is possible to provide a reagent for immunological analysis having an excellent detection sensitivity and capable of avoiding a nonspecific reaction which occurs in conventional methods.