To obtain a zirconium alloy excellent in cold-workability and corrosion resistance and suitable as the material for nuclear fuel cladding duplex tube of a water-cooled type nuclear reactor by specifying its compsn. composed of Sn, Fe, Cr and Zr and further incorporated with Ni and Nb according to necessary.

This is a low Sn-Zr alloy having a compsn. contg., by weight, 0.30 to 0.70% Sn, 0.20 to 0.25% Fe and 0.10 to 0.15% Cr, furthermore contg., at need, one or both of 0.005 to 0.05% Ni and 0.05 to 0.20% Nb, and the balance Zr with inevitable impurities, and in which cracks and strains are not generated even by cold rolling in which the reduction of cross-sectional area is regulated to about ≥80%. By forming an outer tube by this Zr alloy and making an inner tube of a high Sn-Zr alloy contg. 1.2 to 1.7% Sn, the duplex tube for cladding nuclear fuel excellent in corrosion resistance in the outer face in which CSR value defined by the formula of CSR=c/r (c and r denote the strains in the circumferential direction and to strains in the thickness direction) is equal to that of a solid tube of the Zr alloy same as that of the inner tube and having high strength in the whole body can securely be obtd. at a low cost.