The synthesis of spherical poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles with a narrow size distribution was achieved in a dispersant aqueous medium. Various oxidants such as ammonium persulfate, iron(III) p-toluenesulfonate, and iron(111) trichloride were tested. A series of end-functionalized poly(ethylene oxide) (PEO) such as alpha-(3,4-ethylenedioxythiophene) PEO, alpha-(N-methyl pyrrole) PEO, alpha-(fluorene) PEO, alpha,omega-(N-methyl pyrrole) PEO, alpha,omega-(thiophene) PEO, and alpha,omega-(fluorene) PEO were compared as reactive stabilizers. The molar mass and the functionality of these reactive PEOs were found to be important parameters with respect to the control of particle size and size distribution. PEDOT samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AIM), size exclusion chromatography (SEC), and conductivity measurements.