NOVELTY - A solid electrolytic capacitor comprises a valve metal-made anode body on the surface of which are respectively formed a dielectric oxide layer, a composite conductive polymer layer made from a plurality of conductive polymer layers, a carbon layer and a silver layer.    USE - The capacitor can be used e.g. in batteries.    ADVANTAGE - The capacitor has high bonding and mechanical strength, conductivity, capacitance ratio and thermal stability and improved impedance, but low current leakage.    DETAILED DESCRIPTION - The composite conductive polymer layer comprises a first conductive polymer layer of thiophene or its derivative fixed onto the dielectric oxide layer, a second conductive layer of a different polymer formed on it through chemical polymerization, and between the second conductive polymer layer and carbon layer, a number of conductive polymer layers are provided by electrolytic polymerization.    INDEPENDENT CLAIMS are also included for the following: (i) a process for producing the solid electrolytic capacitor by forming the first layer of thiophene or its derivative on the dielectric oxide layer, followed by a second conductive polymer layer of pyrrole, aniline or their derivative by chemical polymerization, and a fourth conductive polymer layer on the second layer through electrolytic polymerization by applying electrodes on the first and second layers; and (ii) a similar process in which a third layer of thiophene or its derivative is formed on the second layer by chemical polymerization and on the third conductive polymer layer a fourth layer is formed through electrolytic polymerization by applying electrodes on the first, second and third layers.    DESCRIPTION OF DRAWING(S) - Longitudinal cross-section of a solid electrolytic capacitor is shown.    Can (1)    Sintered body (4)    Dielectric oxide layer (5)    Carbon layer (7)    Silver layer (8)    Conductive adhesive layer (9)    Cathode terminal plate (10)    Conductive polymer layers (31, 32, 33, 34)