In this study, experiments on generating of CO gas from heated coal samples have been carried out by controlling the atmospheric condition in low O 2 concentration in considering sealed goaf areas at underground coal mines. The laser beam was used to make coal temperature over 60°C within few minutes in order to minimize coal oxidation in heating process. The O 2 concentration in atmosphere is controlled by injecting Air, pure N2, pure CO2 or N2-CO2 mixing gases to simulate a sealed area with an inert gas injected. The results of coal weight reduction ratio and CO gas generation by injecting the mixing gases of 80% N2 and 20% CO2, close to flue gas ratio, have showed similar characteristics with that of N2 gas injection. In addition, the generated CO gas concentration was mainly dependent on coal temperature and O2 concentration.