To obtain a Zr alloy having satisfactory corrosion resistance, that is, superior general corrosion and nodular corrosion resistances even when exposed to a corrosive environment for a longer period of time in correspondence to a tendency to increase the degree of combustion of nuclear fuel and used for a fuel cladding tube and a fuel assembly.

This highly corrosion resistant Zr alloy consists of, by weight, 0.5-1.7% Sn, 0.1-0.3% Fe, 0.05-0.2% Cr, 0.05-2.0% Cu, 0.01-1.0% Nb and the balance Zr with inevitable impurities or further contains 0.01-0.20% Ni.