The crystallization characteristics and recording mechanism of the a-Si (20nm)/Ni (5 nm) bilayer recording film have been studied. Upon heating, the formation of the metastable NiSi phase occurred at about 200oC, followed by the formation of the thermodynamically favored NiSi2 phase at ~ 400oC, and the crystallization of a-Si mediated by the Ni silicides below 600oC, indicating that inserting a thin Ni layer could effectively reduce the crystallization temperature of a-Si. As Si atoms of approximately 92 at% were consumed by NiSi2 phase formation, the reflectivity increase of the a-Si/Ni bilayer recording film was contributed to the formation of NiSi2 phase. The activation energy for Ni silicide formation was determined to be 1.98 eV. The a-Si/Ni bilayer exhibited an optical contrast of 20% and abosrptance of 54%, which can provide high enough CNR and adequate recording sensitivity. After irradiated by a 405 nm blue laser pulse, a recording mark consisting of NiSi2 was clearly formed in the a-Si/Ni bilayer. Under the dynamic test, CNR of 37 dB was achieved at a recording power of 4 mW, demonstrating that the a-Si/Ni bilayer recording film shows a great potential for use in write-once Blu-ray disk.