Phosphorus-containing polyesters can be used in the biomedical field, as they have a wide range of properties. The presence of a phosphate group in the structure of the polyester macrochain makes them suitable for ionic binding of organic substances that exhibit basic properties. A method for hydrolysis of the ethyl phosphate group of polyester had been developed, the isolation of ethanol as a by-product of the reaction had been confirmed by gas chromatography, and optimal conditions for hydrolysis of the polyester side chain had been established, while preserving the main chain of the phosphorus-containing polyester.