Abstract: The relationship between hydrocarbon type composition and oxidation stability of medium lube oil base stocks has been studied. Oils used in this study are the ^#20 turbine oil stock derived from Daqing crude and the solvent-refined and dewaxed medium-heavy gas oil fraction from Huabei crude. It has been found that the polynuclear aromatics in the oils can more significantly enhance the oxidation stability of the white oil than the binuclear aromatics. Both single-ring aromatics and saturated hydrocarbons are oxidation unstable. Resins in the oils, which were found to contain hindered phenols, show some antioxidation properties. The optimum aromatic content as well as the effect of sulfur and nitrogen compounds on oxidation stability have also been investigated. Studies on 2.6-di-tert-butyl-P-cresol (DBPC) responsibility of these two oils indicate that the Huabei oil responds better than the Daqing oil. Sulfur compounds in either oils have a positive effect on DBPC responsibility whereas resins, basic-nitrogen compounds, and single-ring aromatics are on the contrary.