While securing the building-up ability and crack resistance, to provide a build-up wear-resistant copper alloy and valve seat. The build-up wear-resistant copper alloy and valve seat are characterized by having a composition of nickel: 5.0-24.5%, iron: 3.0-20.0%, silicon: 0.5-5.0%, boron: 0.05-0.5%, chromium: 0.3-5.0%, one member or two members or more selected from the group consisting of molybdenum, tungsten and vanadium: 3.0-20.0%, by weight %, and the balance being copper and inevitable impurities.