The invention provides an aqueous eye drop containing latanoprost, a surfactant, and an aliphatic mono- or di-carboxylic acid having a carbon number of 3-10 or a salt thereof. In addition, the invention provides a method of suppressing adsorption of latanoprost to a resin in an aqueous solution, by adding a surfactant and an aliphatic mono- or di-carboxylic acid having a carbon number of 3-10 or a salt thereof.
