Conducting polymers have been investigated widely for use in various applications because of their thermal and environmental stability and good electrical conductivity. As the rate of reaction in chemical oxidative polymerization for the synthesis of conducting polymers is very rapid, it is important to prepare spherical particles of the conducting polymer to maintain the reaction temperature at approximately 278 K. In this study, control of the reaction rate has been investigated, and a new method for the synthesis of polypyrrole particles using a water/oil emulsion is proposed. In this system, the diffusion of the monomer into a water droplet as the dispersed phase is the rate-determining step, and controls the reaction rate at room temperature. Monodispersed spherical polypyrrole particles were synthesized at room temperature using this method. The effects of organic solvent as the continuous phase on the synthesized polypyrrole particle size were also investigated. The diameter of the polypyrrole particle decreased with increasing viscosity of the organic solvent, and an empirical formula connecting the diffusion coefficient and average particle size is proposed.