To develop an ammonia/natural gas co-fired gas turbine, there is a challenge in compliance with environmental regulations of NO x concentration in flue gas. To solve the challenge, power generation tests have been conducted using a 2 MW-class gas turbine with a low NO x combustor. Power generation of 2 MW and a reduction of CO 2 emissions with ammonia mixing ratio of 20% has been achieved. It has been confirmed that the NO x removal device can reduce NO x concentration below 7 ppm. The performance calculation of the heat recovery steam boiler using the measured data as an input value has also been performed. The result showed that the total efficiency of ammonia/natural gas co-fired gas turbine co-generation system can be kept at the same level as a natural gas fired system.