Biodiesel is defined as the monoalkyl ester derivative of long-chain fatty acids, originated from renewable sources, such as vegetable oils or animal fats. The most common use of biodiesel is direct substitution of fossil fuels in compression-ignition engines. The heating of vegetable oils can cause complementary decomposition reactions, in which the results can also lead to the formation of polymeric compounds. This work has been carried out to study the degradation process of biodiesel in different temperatures and exposure times. The degradation process of biodiesel affected its thermogravimetric and calorimetric profiles, indicating the formation of intermediary compounds. The spectroscopic data of degraded biodiesel suggested oxidative polymerization, confirming thermal data. In the degraded biodiesel at 210 degrees C for 48 h, the formation of gum occurred, indicating that oxidative polymerization was completed.