The present disclosure relates to a composition for preparing a vinyl chloride-based polymer and a method of preparing a vinyl chloride-based polymer using the same, and provides the composition giving excellent productivity for preparing a vinyl chloride-based polymer includes while maintaining excellent foaming and viscosity properties of a plastisol including the prepared vinyl chloride-based polymer, by including a pH regulator composed of a carbonate-based metal salt, and a transition metal catalyst in the composition, and controlling an amount of the transition metal catalyst, and controlling an amount of a reducing agent such that a trace amount or none of the reducing agent is included, and the method of preparing a vinyl chloride-based polymer using the same.