We investigate the magnetic properties of nanocrystalline Fe73.5Cu1M3Si13.5B9 (M = Nb or Mo) alloys when C is substituted for B up to 2 at%. It is found that the permeability and coercivity deteriorate with the content of C in the case of both M = Nb and Mo. The saturation magnetization also deteriorates as C is substituted for B in the case of M = Mo but it improves linearly with the C content in the case of M = Nb. This increase in the saturation magnetization of the Fe-Cu-Nb-Si-B alloy with C addition can provide an opportunity to overcome one of the main disadvantages, low magnetic flux density, of the alloy. In the latter part of the work we also investigate the magnetic properties of Fe76.5-yCu1 Nb(y) (Si0.5B0.4C0.1)22.5 (0 less-than-or-equal-to y less-than-or-equal-to 3) alloys, particular emphasis being given to the role of Nb in the presence of C. It is found that C may help Nb to suppress the growth of alpha-Fe grains in the alloy.