The electrical properties and high-temperature characteristics of an electrolytic capacitor are rendered satisfactory by addition of a compound with an unsaturated bond-containing chain which serves to absorb hydrogen gas generated by reaction between the aluminum electrode foil and the electrolyte solution. The electrolytic capacitor contains the unsaturated compound which allows hydrogen addition, or the electrolytic solution, which comprises a solvent composed of 10-80 wt % of an organic solvent and 90-20 wt % water and at least one electrolyte selected from the group consisting of carboxylic acids or their salts and inorganic acids or their salts, also comprises one or more unsaturated compounds which are water-soluble or soluble in polar and protic polar solvents.