Mixing of Ag ion-doped polyethyleneimine (PEI) and polyacrylic acid (PAA) produced Ag ion-doped polyelectrolyte complex particles (PECs) in solution. Positively charged Ag ion-doped PECs (Ag ion-PECs) with a spherical shape were deposited alternatively with PAA to form a multilayer assembly. The multilayered film containing Ag ion-PECs was reduced to generate a composite nanostructure. Metal nanoparticles (NP)-enriched nanocomposite films were formed by an additional process of post-adsorption of precursors on PECs within the nanocomposite films, which resulted in the enhancement of the catalytic and electrical properties of the composite films. Because the films contain PECs that are responsive to changes in pH and most of the NPs are embedded in the PECs, interesting catalytic properties, which are unexpected in a particle-typed catalyst, were observed upon pH changes. As a result of the reversible structural changes of the films and the immobilisation of the NPs within the films, the film-type catalysts showed enhanced performance and stability during catalytic reactions under various pH conditions, compared to particle-type catalysts.