The characteristics of a tantalum capacitor using polypyrrole instead of MnO₂ as a solid electrolyte were studied. The polypyrrole layer was prepared by applying electrochemical oxidative polymerization galvanostatically in an aqueous solution dissolving sodium p-toluenesulfonate as a dopant. In this case an external electrode was applied to the surface of a tantalum pellet pre-coated with polypyrrole by chemical oxidative polymerization in order to give conductive property to the dielectric film because of its insulation property. It was identified that the equivalent series resistance of the reaction system decreased as the increase of the concentration of monomer pyrrole in an electrolyte and the initial polymerization on most reaction sites of the dielectric inside the pores was not completed until the ESR reached a minimum value. It was obtained from the analysis on the relation of a pyrrole monomer concentration ranged from 0.05 to 1.5 mol/l and a polymerization time ranged from 1 to 5 hours that there were a critical concentration and a critical polymerization time to achieve a high degree of pore filling with polypyrrole and to form a uniform polypyrrole layer from inside parts to outside parts of the sintered pellet. The tantalum capacitor polymerized with a concentration of 0.5 mol/l pyrrole for 4 hours was recorded the best properties finally.