CdS nanoparticles have been synthesized in aqueous solution using polyvinyl alcohol (PVA) as a capping reagent. The effects of exposure by ultraviolet (UV) light on optical properties of nanocomposites consisting of colloidal CdS nanoparticles and a polymer PVA matrix were studied by employing photoluminescence (PL) spectroscopy. It is shown that UV-induced changes of the photoluminescence intensity in PVA are caused by creation and healing of non-radiative recombination centers. It is also concluded that in the nanocomposites, the UV-induced changes of the PL intensity are predominantly governed by processes at the NP/PVA interface.