This article investigates the hydrolytic stability for diisooctyl sebacate (DOS), the pentaerythritol and diethylene glycol esters of a C/sub 5/-C/sub 9/ synthetic fatty acid cut (PEE and DEGE), and synthetic oils based on these esters: VNII NP 50-1-4f, B-3V, and 36/1 KU-A. The hydrolysis rate was evaluated from the increase in concentration of acid formed in the process of hydrolysis at specific intervals of time. The dependence of the degree of hydrolysis on the content of water in the oil is examined. The results of the study of the hydrolytic stability of esters and synthetic oils show that the indexes most susceptible to change in the course of hydrolysis are the acid number of the oil and the pH and acid number of the water extract. The stability of the kinematic viscosity at /sup -/40/sup 0/C before and after hydrolysis and the absence of sludge after hydrolysis indicate that in the hydrolysis under these conditions, thermal and thermal-oxidative processes have practically no influence on the oil properties. It is determined that the low hydrolytic stability of the USSR diester oils is due to their content of certain additives that catalyze hydrolysis.