An object of the present invention is to provide an electrolyte for an electrolytic capacitor, which is advantageous not only in that both electric conductivity and withstand voltage property are high, but also in that thermal stability is excellent, and an electrolytic capacitor using the electrolyte. Specifically, the present invention provides an electrolyte for an electrolytic capacitor, comprising a solvent, at least one quaternary amidinium salt selected from the group consisting of a quaternary amidinium salt of a hydroxy-substituted aromatic monocarboxylic acid and a quaternary amidinium salt of phthalic acid, and metal oxide particles, and an electrolytic capacitor using the electrolyte.