The present invention provides a solid electrolytic capacitor having a low ESR, excellent heat resistance, and reliability used under a high temperature condition. On the dielectric layer of the capacitor element, 2-alkyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine monomer is subject to oxidation polymerization to provide a first conductive polymer layer. Then, 2,3-dihydro-thieno[3,4-b][1,4]dioxine or a monomer mixture of 2,3-dihydro-thieno[3,4-b][1,4]dioxine and 2-alkyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine is subject to oxidation polymerization to provide a second conductive polymer layer. The formation of the first conductive polymer layer and the second conductive polymer layer is alternatively repeated. The first conductive polymer and the second conductive polymer serve as a solid electrolyte to provide a solid electrolytic.