The influence of the UV irradiation on the morphology and optical properties of nanosize colloidal silver particles formed in the poly(vinyl alcohol) matrix containing Ag+ and formic acid was investigated. Formation of both filament and ultrafine silver particles accompanied by a strong blue shift of the silver plasmon absorption band from 425 to 385 nm was observed under UV irradiation. The mechanism of the electron accumulation on silver particles is proposed to explain the observed morphological and spectral changes.