Chitosan thin films with controlled thickness have been fabricated by spin-coating chitosan acetate and citrate solutions for application as planar optical waveguides (POW). "In situ" reduction of preadsorbed in chitosan film Ag+ ions with sodium borohydride resulted in formation of chitosan/Ag composites, in which silver nanoparticles of a size below 10 nm were homogeneously distributed. In contrast to chitosan/Ag composites formed in solution, UV-vis spectra of the thin film composites have depicted a single narrow adsorption band at 412-413 nm independently of the silver content. The absence of long-wavelength shoulders in the spectra, which are associated with oscillations of non-spherical particles or plasmon coupling of aggregates, has confirmed SEM data on high uniformity of the Ag/chitosan composite films. We have shown that the refractive index of the composites at a wavelength of a HeNe laser (633 nm) increases from 1.53 to 1.69 with the increase of the silver volume fraction up to 2.55%. Investigations of composites waveguiding properties revealed that the light propagation is feasible up to a silver volume fraction of 1.3%, which corresponds to the maximum refractive index 1.58. (C) 2014 Elsevier B.V. All rights reserved.