A 150-MW, 1300°C (1573 K) class gas turbine combustor firing coalgasified fuel has been designed. Main purpose of the present paper is first to estimate CO and NOx emissions, and second to discuss the low NOx combusion technology burning such a low-BTU gas. The full-scale, atmospheric-pressure combustion tests were conducted over a wide range of conditions using bypass air. The results are summarized as follows: (1) A designed combustor has an excellent combustion efficiency of 99.6 percent even when the calorific value of fuel drops to 650 kcal/m3 N. (2) CO and NOx emissions can be estimated by the air ratio in primary combustion zone. (3) The role of air bypass valve is important for low NOx combustion, and to give stable combustion at lower load conditions. (4) Ammonia conversion to NOx is minimized with a optimum air ratio in primary combustion zone.