A superconducting copper matrix wire containing many filaments of 0.4‐mil‐diam Nb3Sn has been prepared and tested. The critical current in transverse magnetic fields in the range of 50–100 kG is 3–5 times greater than that of the Nb–Ti alloy but not as high as that of the best Nb3Sn. The critical temperature of this material is about 17°K.