Superconductor-clad composite wires, which consist of copper as a stabilizer and Nb-62.5Ti-2.5Zr superconducting ternary alloy on it, are studied on A. C. loss, I-V characteristics and coil simulation test. The copper inside the superconductor does not contribute to the A. C. loss. The maximum thickness of the copper layer outside the superconductor not to give a considerable loss is also discussed. The I-V characteristics and the results of coil simulation test show that the superconductor-clad composite wires are almost stable, though a part of the copper exists inside the superconductor.