Abstract: The study on thermo-oxidation behavior of polybutadienes with different contents of 1,2-units shows that the thermo-oxidation reaction takes place more easily at the doble bond in the main chain than in the side vinyl group of polybutadiene,as being attributed to having more α-H's in the former case. Based on the thermo-oxidation temperatureand apparent activation energy E, it has been concluded that the syndiotactic 1,2-polybutadiene with high vinyl content synthesized on the cobolt catalyst system is more stable than that obtained with molybdenum catalyst system. The E of the former is more than 150kJ/mol, but -100kJ/mol for the latter. The variation is considered due to the difference in macromolecular aggregatoin.