A process for producing a vinyl chloride-based polymer by suspension polymerization is provided. The polymerization is initiated in the presence of (A) a particular hydroxypropylmethylcellulose, (B) a particular partially saponified PVA with a saponification degree of 75 to 85 mol % and an average polymerization degree of 1000 to 3000, and (C) a particular partially saponified PVA with a saponification degree of 20 to 57 mol % and an average polymerization degree of 150 to 600 in a specified ration, and said (C) is also additionally added to the polymerization system when a conversion rate is 15-50%. Polymers with a high porosity, excellent plasticizer absorption, extremely low levels of fish eyes, and a high bulk specific gravity are produced at a high level of productivity.