Fuel-NOx concentrations under the conditions of high CO_2 concentration have been experimentally investigated with a tubular flame burner. At first, flame stability limits are examined for CH_4/O_2/CO_2 mixture with a flat flame burner as well as a tubular flame burner. Results show that, for CO_2-dilution mixture, a flame can be established on a flat flame burner when O_2 concentration in oxidizer is greater than 26%. On the other hand, a tubular flame can be established in wide range of φ even O_2 concentration in oxidizer is 21% O_2. The results of NOx measurement showed that the Fuel-NOx concentration large for lean to stoichiometric condition. The results also showed that the Fuel-NOx concentration of 32% O_2 CO_2-diluted mixture is almost identical with that of air combustion, and NOx concentration drastically decreases with decreasing oxygen concentration in oxidizer.