The present invention provides a method of purifying a vinyl polymer to be used as a component of a composition capable of undergoing hydrosilylation.The present invention provides a vinyl polymers obtainable by atom transfer radical polymerization can be purified economically and efficiently by adsorption treatment using an acidic adsorbent and a basic adsorbent combinedly, with the result that the reactivity in hydrosilylation thereof is improved. Thus, the polymers can be used as components in hydrosilylation reaction-susceptible compositions.