An electrolytic solution for Karl Fischer coulometric titration is disclosed which consists mainly of an amine, sulfur dioxide, iodide ions, and a solvent which is a mixed solvent comprising (a) propylene carbonate and (b) a dialkylene glycol monoalkyl ether (wherein the alkylene groups and the alkyl group each have from 1 to 4 carbon atoms). The electrolytic solution, which is based on a less toxic solvent, has fewer side reactions with ketones and is useful in accurately determining the water content of ketones.