The alcoholytic destruction of poly(ethylene terephthalate) (PET) with diethylene glycol (DEG) is studied. The influence of the DEG amount on the structure of the obtained oligoesters is investigated. On the basis of the experimental results, a probable mechanism is proposed for the alcoholysis of PET at large excess of DEG. The molecular weight characteristics of the obtained oligomers are studied and kinetic schemes are assumed for alcoholysis at different molar ratios of the starting components. Optimal conditions are established for the preparation of linear oligoester diols suitable for the synthesis of water-borne polyurethanes.