A method for solubilizing a pyridonecarboxylic acid or a pharmacologically acceptable salt thereof, which comprises adding an arylcarboxylic acid of the formula (I):L.sup.1 --R.sup.1 COOH (I)wherein L.sup.1 is an optionally substituted heterocyclic group or aryl group having not more than 14 carbon atoms, and R.sup.1 is an optionally substituted alkyl group having not more than 4 carbon atoms or a single bond, to the pyridonecarboxylic acid or the pharmacologically acceptable salt thereof, a solubilizer thereof and an aqueous solution containing a solubilized pyridonecarboxylic acid. According to the solubilization method of the present invention, the solubility of pyridonecarboxylic acid compounds and salts thereof at near physiological pH can be increased, thereby making the production of an aqueous solution to be used as an eye drop, nasal drop, ear drop and the like possible.