In this investigation, nickel powders were prepared at various synthetic conditions with hydrazine hydrate from aqueous nickel chloride solution containing 40 vol% of ethanol using the conventional and ultrasonic hydro-thermal synthetic method. It was found that ultrasonic cavity effect and synthetic conditions affected the formation of nickel powders by the means of X-ray diffraction, scanning electron microscopy, thermal gravimetry analysis, and X-ray photoelectron spectroscopy analyses. Compared to the conventional hydro-thermal synthesis, a shorter reduction time, a smaller average particle size, and more uniform distribution of particle size were obtained in the ultrasonic hydro-thermal synthesis, due to the cavitations effect of ultrasonic.