The present invention provides an antistatic agent for vinyl chloride-based resins which can impart superior antistatic properties to the vinyl chloride-based resin, and which can thereby solve various problems arising from charging of the vinyl chloride-based resin with static electricity, a vinyl chloride-based resin composition containing this antistatic agent, and a method for manufacturing this composition. The present invention provides an antistatic agent for vinyl chloride-based resins which consists of silica particles containing at least 99.0% by mass of SiO.sub.2 and 0.00005% 80.5 ppm by mass or less of sodium, and which has such a particle size distribution that at least 98% by mass of the silica particles is occupied by the particles having a particle diameter in the range from 30 to 1,000 nm.