Abstract Thermogravimetric-Mass Spectroscopy (TG-MS) study on lignin decomposition under different (oxygen-containing) atmospheres was carried out to investigate thermal performance of lignin during pyrolysis, oxidative gasification, oxy/fuel combustion and CO2 gasification. Only one significant mass loss stage was observed for lignin decomposition under helium (He), while another stage, representing char oxidation, appeared under oxygen and CO2 conditions. No significant variation of the activation energy was presented for the first pyrolysis stage under different atmospheres (from 40.4 to 53.2kJ/mol). A much higher temperature was required for char oxidation under CO2 than those under O2 atmospheres, giving the activation energy of 541.9kJ/mol as compared to around 160kJ/mol for O2-containing atmospheres. The evolution profiles of CO and CO2 under different atmospheres were in good accordance with the DTG curves regardless of atmospheres.