In this study ZnO nanoparticles have been prepared by sonochemical method (also known as sonochemitry). The aim of using this method is the simplicity of obtaining nanoparticles in small times and without using any heating to initiate the chemical reaction. Different with other traditional chemical methods, the sonochemical method is based on acoustic cavitations. The formation, growth and collapse of bubbles in the liquid were generating localized hot spots with very high temperatures of 5000–25,000 K. These temperatures are enough to initiate the chemical reaction. ZnO nanoparticles with sizes in the range (28- 24 nm) are obtained by changing the time of sonication, the time period in which the suspension was exposed to Ultrasound waves. The optical band gap which obtained from UV measurements was found to be about 3.1 eV for all samples and the characteristic band gap of ZnO was at around 560 cm-1.