Functionally Graded Material (FGM) has the potential to endure in a deep well and sour environment. Japan National Oil Corporation (JNOC), Japan Research and Development Center for Metals (JRCM) and Sumitomo Electric Industries, Ltd. (SEI) applied FGM to a stabilizer blade and then developed a prototype stabilizer with it. This FGM is composed of Cobalt- composition graded cemented carbide layers and a steel substrate with lower Co composition in the surface. The graded cemented carbide powders stacked on steel were sinter-bonded by pulse-current resistance heating. We manufactured the desired structure and confirmed the stress relief, high bonding strength, and distribution of functionality of coated layers between the surface (with high wear resistance) and the inside (with high toughness). The new stabilizer, with FGM blades composed of WC-25%Co (thickness of the layer is 1.5mm) and WC-40%Co (thickness of layer is 1.5mm), was tested in the Kashiwazaki Test Field (KTF) well and in the Ministry of International Trade and Industry's (MITI) Sanriku-oki well in Japan. To compare a conventional type of stabilizer which has cemented carbide buttons with this new stabilizer, we drilled with both stabilizers for about 270m in the KTF well and for about 980m in the MITI well. The wear resistance of FGM blade was more than 2 times that of the conventional blade in the KTF well and more than 20 times higher in the MITI well. These results suggest that we might expect the new stabilizer to have high performance in deep wells and to achieve at least twice the tool life of conventional stabilizers while drilling.