Ductile alloys which have approximately equal amounts of Co and Fe, plus Ni and a small amount of Nb were investigated for remanent reed switch applications. As a result, 39Fe&sngbnd;38Co&sngbnd;20N&sngbnd;3Nb wire 0.6mm in diameter, made by intermediate annealing at 700°C, cold drawing to 92% reduction in area, and final annealing at 6007deg;C for 1 hour, showed a coercive force of 30 Oe, remanence of 16000 G, squareness ratio higher than 0.95, and thermal expansion coefficient of98×10−7/°Cbetween 30 and 400°C. This alloy could be cold‐worked easily after annealing. The phase was f.c.c. after annealing at a temperature over 800°C. However, cold working caused partial phase transformation of f.c.c. into b.c.c. This intermixing of f.c.c. and b.c.c. phases in a high coercive force state survived up to 700°C annealing. On the other hand, remanence was low in the cold drawn state, but increased by annealing over 600°C. The coercive force grew larger as the Nb content increased.