In the present study ZnO nanoparticles have been synthesized using sonochemical technique at different ultrasonic exposure power. The powers were 20%, 40% and 60% of the total power of ultrasonic generator (operating at 20 kHz with a maximum power output of 250 W). The experimental procedures were carried out in Ultrasonic Lab, National Institute for Standards, Egypt. ZnO nanoparticles samples were investigated by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), UV visible Absorption and Fourier Transform Infrared Spectroscopy (FTIR). XRD and TEM results reveal that Exposure power has a pronounced effect on both particle size as well as morphology. The greater the exposure power, the larger the particle size. In addition, the morphology of ZnO nanoparticles modified from rod-like shape to semi-spherical shape by raising the exposure power. The band gap for all samples estimated by UV absorption data was found to be around 3.1 eV. The ZnO absorption band was observed at 560 cm-1 in FTIR spectra.