We report the results on the growth behaviors of electroless pure nickel thin films on Si(001) substrates from a systematic investigation. Continuous pure Ni films with a polycrystalline structure were successfully plated on the surfaces of Si substrates using the hydrazine-modified electroless Ni deposition processes. The thicknesses of the pure Ni films can be controlled by tuning the electroless plating temperature and time. The deposition rate of the electroless pure Ni films increased exponentially with the plating temperatures. The activation energy of the electroless pure Ni deposition on Si(001) substrate for samples plated at 55-75 degrees C could be calculated from an Arrhenius plot, and it was about 0.95 eV/atom.