Unlike oxidative degradation of lubricants, tribology-induced degradation is rarely studied. In this work, the tribological performance and oxidative stability of ester-based lubricants were evaluated before and after tribological testing. Results showed that the tribological performances of base oils are highly dependent on the lubricant formulation and test conditions. Tribological processes could cause detrimental effects on oxidative stability even under moderate conditions. The addition of antiwear additives seems to effectively inhibit the chemically breakdown of esters by forming a protective film. Mechanical shearing, high temperature in contact zones, catalytic effect of nascent surface, wear debris, as well as self- catalysis are the major reasons that are responsible for the oxidative deterioration of the lubricant after tribological testing.