We have examined optical absorption properties of the composite nanoparticles consisting of Ag core coated with the J-aggregate of 3,3′-disulfopropyl-5,5′-dichlorothiacyanine sodium salt (TC) in aqueous suspensions and in self-assembled (SA) films on the quartz plates. Four kinds of SA films were fabricated by the alternate adsorption technique; the monolayer SA films in which Ag:TC composite nanoparticles were sparsely (S film) or densely (D film) packed on the surface, and the multilayer SA films composed of D films and thin (SAS film) or thick (SAL film) spacer layers. Based on the absorption spectra and the atomic force microscopic images of those films, the existence of electromagnetic interaction between densely packed Ag:TC nanoparticles in the single layers, as well as between adjacent layers incorporating those nanoparticles has been suggested.