PURPOSE: To obtain the subject resin excellent in moldability, coloring preventing property, impact resistance and heat resistance and useful for heat-resistant pipes, heat-resistant valves, etc.

CONSTITUTION: A chlorinated vinyl chloride resin having 60-64% chlorine content is chlorinated in a state suspended in an aqueous medium so that chlorine content may be ≥66% to provide the objective resin. Furthermore, this resin can also be obtained by once stopping chlorination when chlorine content of a vinyl chloride-based resin became 60-64% by chlorination and separating the chlorinated vinyl chloride resin having 60-64% chlorine content, suspending this chlorinated vinyl chloride in an aqueous medium and chlorinating the chlorinated vinyl chloride so that the chlorine content may become ≥66%.