Organosilica nanomaterials have received substantial attention in the past two decades with a number of reports describing their synthesis, structural features, properties and applications. Silica nanoparticles are often synthesised using so-called Stober method, which involves base- or acid-catalysed hydrolysis of alkyl silicates in alcohol or alcohol-media. We have developed a novel approach for the synthesis of hybrid polymer-containing silica nanoparticles by condensation of 3-mercaptopropyltrimethodxysilane in the presence of a water-soluble polymer(hydroxyethylcellulose) in aprotic medium (dimethylsulfoxide). This process results in colloidally-stable particles, whose size can be controlled by the content of hydroxyethylcellulose in the reaction mixture. The aim of this experient is to establish the structural features of these particles.