Abstract: The unreacted gaseous vinyl chloride monomer still remaining in a polymerization reactor from which the polymerizate has been removed can be discharged by blowing steam into the reactor from its top so that the gaseous monomer is pushed downward and moved out from the bottom of the reactor, followed by a conventional treatment for condensation. This method of discharge serves to put the reactor open to the ambient atmosphere without the emission of the unreacted monomer and, as such, solve the problems of the workers' health and environmental pollution.