The kinetics of the nanocrystallization of amorphous Fe81B13.5Si3.5C2 ribbon is studied. The changes in the microstructures and magnetic properties of ribbons annealed at 425 and 495 degrees C for 0.5-10 h were investigated using an X-ray diffractometer (XRD), Mossbauer spectroscopy (MS), differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM). The changes in the surface morphology were observed by a changed atomic force microscope (AFM). The XRD patterns and the Mossbauer spectrums show the formation of nanocrystallites of alpha-Fe(Si), Fe-B, Fe3C and Fe3Si of different grain sizes when annealed at different temperatures. The nanocrystallization kinetics of the Fe81B13.5Si3.5C2 ribbon are described by an Avrami growth curve with an exponent values of 1.34 and 1.01 for the isothermal annealing at 425 and 495 degrees C, respectively. AFM topography pictures and surface image show that the density of the microstructure and the size of the grain increase as higher annealing temperatures are used. (C) 2007 Elsevier Ltd. All rights reserved.