In developing large-capacity gas turbine for use in power generation as the main machines in combined cycle power plants, Mitsubishi Heavy Industries, Ltd. (MHI) has made every effort to increase thermal efficiency. However, the global environment is growing into a serious problem day by day, as evidenced by frequent news reports of unusual weather attributable to global warming. Under such conditions, Japan is certainly required to achieve the goal of reducing the emission of greenhouse gases such as CO₂, under the Kyoto Protocol that came into effect in February this year. Against this background, a national project to develop the component technologies for a 1700°C class high efficiency gas turbine was started in fiscal year 2004 with schedule to complete in four years. MHI participates in this project and has started the development work allocated to them. When the 1700°C class gas Turbine is commercialized, it will become possible to reduce the overall emission of CO₂ in Japan by 0.4 %, if all the 1.25 million kW coal-firing power stations operating in Japan are replaced by combined cycle power plants equipped with the 1700°C class gas Turbine. This reduction effect is quite significant when compared to the 6 % reduction targeted by the Kyoto Protocol. Accordingly, this effect brought by the development of the 1700°C class high efficiency gas Turbine will spread not only to Japan but also to the world, so that it is expected to contribute to an improvement in the global environment. This paper introduces the results and future plan of development project for component technologies of this gas turbine.