To eliminate a halogen group of a halogen group-terminated vinyl polymer, the present invention provides a method to treat said polymer with an oxy anion compound to thereby eliminate a terminal halogen group easily. Thus, it is possible to improve the storage stability of the polymer or a curable composition comprising said polymer and to prevent various materials coming into contact with the reaction apparatus or the polymer from being corroded. In particular, it is possible to improve the storage stability of a crosslinkable silyl group-containing polymer.