The present invention provides: a process for preparing a vinyl polymer containing a halogen in an amount of 1,000 mg or less per kilogram, in which a vinyl polymer containing the halogen produced by atom transfer radical polymerization of a vinyl monomer is heated at a temperature in the range of 140 to 250.degree. C. to dehalogenate the vinyl polymer; a vinyl polymer obtained by the process; and a hydrosilylation-reactive curable composition containing the vinyl polymer.