In this paper, we report the effect of partially replaced Nb on glass forming ability (GFA), structure and soft magnetic properties in Fe86Zr7−xNbxB6Cu1 (x = 0 and 3.5 at.%) melt spun ribbons, processed at different cooling rates by varying wheel speeds. Decreasing the wheel speed, the structures of both alloys change from complete amorphous to partial amorphous then to complete crystalline phase. It has been found that the Nb enhances GFA which is also confirmed through thermodynamically calculated PHSS values. The annealing of completely amorphous ribbons of both compositions, processed at a wheel speed of 47 m/s leads to the formation of α-Fe phase in amorphous matrix and enhances soft magnetic properties. © 2015, The Indian Institute of Metals - IIM.