The amorphous Fe78Si9B13 alloy was treated by low frequency pulse magnetic field (LFPMF). The microstructure was observed by Mössbauer spectroscopy and Transmission Electron Microscope. The activation energy of nanocrystallization of amorphous alloy Fe78Si9B13 treated by low frequency pulse magnetic field was determined by differential scanning calorimetry (DSC). The results indicated that the activation energy was decreased from 433.6kJ.mol-1 to less than 200kJ.mol-1 after LFPMF. The nucleating rate of α-Fe(Si) was increased and there was only single phase α-Fe(Si) crystalline formed.