Abstract: The soft magnetic properties are reported for newly-developed nanocrystalline Fe72.7Cu1Nb1.8-Mo2Si13B9.5 and Fe73Cu1Nb1.5Mo2Si13B9.5. The high frequency core losses of the new alloys are as follows: P3/100K=473 kW·m-3, P2/200K=750 kW·m-3, P2/500K=3400 kW·m-3,P0.5/1000K=680 kW·m-3, which are clearly lower than those of the early-developed Fe-Cu-Nb-Si-B nanocrystalline alloys and the superior power MnZn ferrite H7.4. The dependences ofcore loss on frequency and amplitude magnetic flux density have been analysed. The temperature relations of initial susceptibility have been examined for as-quenched and different annealedFe72.7Cu1Nb1.8Mo2Si13B9.5 alloy and interpreted by using the phenomenological theory.