A method for determination of adipic acid in the product of its polycondensation with butane-1,4-diamine in aqueous medium has been developed. The acid is isolated from the reaction mixture by liquid-liquid extraction, then derivatized with diazomethane and the resulting dimethyl ester is analyzed by GLC. The presence of water does not influence the analysis. The method can be used for determination of the adipic acid in the reaction mixture ranging from 0.5 to 100 %.