Provided is an electrolytic solution for an aluminum electrolytic capacitor, which shows a specific conductivity, a high sparking voltage, and a characteristic of causing only a slight expansion of the capacitor in the reflow process, each being comparable with conventional alkyl phosphate anions, and which has high reliability without causing a short circuit. Also provided is an aluminum electrolytic capacitor. The present invention is directed to an electrolytic solution for an aluminum electrolytic capacitor, comprising an electrolyte (C) comprising an alkyl phosphate anion (a) represented by the general formula (1)/(2) and an amidinium cation (b); a borate ester (H) which is obtained by reacting boric acid (d) with diethylene glycol (e) and a polyalkylene glycol (f) having a molecular weight of 130-350 and/or a polyalkylene glycol monoalkyl ether (g) having a molecular weight of 130-350, and which has a boron content of 5-14 wt %; and an organic solvent (J).