Combustion properties of coal gasification gas with CO 2dilution were investigated for a newly proposed IGCC power generation system with CO 2 capture. In this system, the gasification gas was burned under high CO 2 concentration atmosphere. In order to clarify the properties of the flames under such atmosphere, the laminar and turbulent burning velocities were investigated for outwardly propagating stoichiometric H 2/O 2/CO 2 and H 2/O 2/N 2 flames under the two conditions, 1: the same amount of diluent of CO 2 or N 2, 2: the constant flame temperature irrespective of diluents. Under the condition1 of the same amount of diluents, the unstretched laminar burning velocities, u l of CO 2 diluted flames were smaller than those of N 2 diluted flames. The ratios of the turbulent burning velocity at the flame radius 30mm, u tn(30mm)to u l of the CO 2 diluted flames were found to be larger than those of N 2 diluted flames. Under the condition2 of the constant flame temperature, it was set to 1300, 1500, 1700, and 2135 degrees Celsius. At the flame temperatures except for 2135 degrees Celsius, u l of CO 2 diluted flames were slightly smaller than those of N 2 diluted flames. The ratios, u tn(30mm) / u lof CO 2 diluted flames were larger than those of N 2 diluted flames. Increase in the turbulence Karlovitz number and decrease in the Markstein number by the CO 2 dilution might cause the increase in u tn(30mm) / u l of CO 2 diluted flames in both conditions.