A thermal plasma process for the recovery and reduction of nickel oxide in the spent nickel-based catalyst (NiO/SiO2) was developed. The spent catalyst was sintered at >1,500 degrees C under plasma condition and the nickel oxide therein was reduced to nickel, which was proven by XRD and EDX. By application of SEM and GC technique, the organic tar on the surface of the spent catalyst was found to decomposed and converted to syngas (CO, CO2, and H-2), which might be the reducing agents in the process. A gasification mechanism for the generation of syngas and the reduction of nickel oxide under plasma conditions was proposed.