Crystallisation behaviour and magnetic properties of as-spun and annealed Fe40Co40Cu0.5Zr9Al 2Si4B4.5 alloy have been studied. The annealing was performed at 873K for 15min. XRD and TEM studies shows the formation of nanocrystalline α-(Fe,Co)(SiAl) particles with 7.5±2nm in diameter dispersed in an amorphous matrix. The Curie temperature of the as-spun amorphous ribbon is 736K. Saturation magnetisation of the annealed sample decreases at a rate of 0.5emu/g/K in the measured temperature range of 300-1000K. Excellent room temperature AC magnetic properties are achieved for the nanocrystalline sample. The low value of the imaginary part of the permeability and the high cut-off frequency (20kHz) suggest that the eddy current contribution in the annealed materials is low. The coercivity of the annealed sample remains almost constant at 95A/m up to the frequency of 20kHz. High saturation magnetisation, high Curie temperature and excellent soft magnetic properties in the nanocrystalline state suggests that Fe40Co40Cu 0.5Zr9Al2Si4B4.5 alloy is a strong candidate for high temperature magnetic application. © 2004 Elsevier B.V. All rights reserved.