Disclosed are an aluminum electrolytic capacitor having low impedance properties and a long service life, and an electrolytic solution which enables to give such capacitor. The electrolytic solution contains a solvent containing water, a phosphorus oxoacid ion-generating compound which can generate a phosphorus oxoacid ion in an aqueous solution, and a chelating agent which can coordinate with aluminum to form an aqueous aluminum chelate complex. The electrolytic solution further contains a compound selected from the group consisting of azelaic acid and an azelaic acid salt, and a compound selected from the group consisting of formic acid, a formic acid salt, adipic acid, an adipic acid salt, glutaric acid and a glutaric acid salt. The content of azelaic acid and/or the azelaic acid salt is at least 0.03 moles per kg of the solvent. When the electrolytic solution is used in an electrolytic capacitor which utilizes an anode having an aluminum oxide film containing phosphorus in an amount of 30 to 150 mg per unit CV product in terms of phosphoric acid, the service life of the capacitor is remarkably prolonged.