Ketocarboxylic acids such as levulinic acid can be efficiently purified in high yield by esterification with a hydrocarbon polyol to the corresponding polyketocarboxylic ester, which can be readily purified, for example recrystallized. After purification, the ketocarboxylic ester can be hydrolyzed to provide pure ketocarboxylic acid, or a salt thereof, after removal of the esterifying hydrocarbon polyol, or used for other synthetic transformations. Advantageously, the polyketocarboxylic esters, ketocarboxylic acids, and salts thereof produced by this method are obtained in high purity.