Abstract Polythiophene (PT) nanoparticles with regular spherical morphology, which were not commonly observed in traditional iron(III) catalyzed oxidative polymerization of thiophene in organic solvents, have been synthesized by copper(II) catalyzed oxidative emulsion polymerization with high yields in aqueous medium. Different copper(II) salts were shown to have significant influence on the rate of polymerization as well as the properties and the morphology of PT. Cupric nitrate, cupric sulfate and cupric chloride are found efficient to catalyze the polymerization, and spherical PT particles with diameters of 60–100 nm were prepared with high yields (86–98%). While using cupric bromide only lead to irregular products with relatively low yield (39%). The different effects of these copper salts on the surface resistivity and thermal stability of the product were also discussed. Additionally, sodium dodecyl sulfonate as anionic surfactant was found capable of increasing the polymer thermal stability for this aqueous polymerization system.