An immunogenic composition comprising as an effective ingredient an antigen-adjuvant microparticle complex containing an antigen encapsulated in an adjuvant microparticle composed of an amphiphilic polymer(s) whose hydrophobic segment is a poly(hydroxy acid), or a particle composed of the antigen-adjuvant microparticle complex associated together, can induce a high immune response against the antigen even with a small amount of the antigen and a small number of doses, so that the immunogenic composition is useful as a vaccine effective for therapy and prophylaxis of infectious diseases, cancer and the like.
