To obtain a separating agent for separating polybasic carboxylic acids by disposing two or ore specific forming potions in a compound.

This agent for separating polybasic carboxylic acids comprises a compound having two or more coordination bond-forming portions. The coordination bond-forming portions are preferably nitrogen-containing heterocyclic rings having ligands, respectively. The nitrogen-containing rings include phenanthroline rings and pyridine rings. The compound is preferably a compound of formula I, II, III, IV or V, etc. A method for using the separating agent to form the coordination polymer-like complex of the polybasic carboxylic acid comprises adding the separating agent in a solid state such as powder as such or in a solution state dissolved in acetic acid to the polybasic carboxylic acid dissolved in water, namely an aqueous solution containing the polybasic carboxylic acid. The polybasic carboxylic acid and the condensing agent form the coordination polymer-like complex. The complex can be precipitated, coagulated or gelled in the reaction solution and separated. The polybasic carboxylic acid can again be isolated from the complex.