© 2016 Trans Tech Publications, Switzerland. ZnO nanoparticles were successfully synthesized via the co-precipitation method using zinc nitrate and sodium hydroxide as raw materials. Size and shape of ZnO nanoparticles were well controlled by varying the ratio of sodium hydroxide solutions (0.5-0.9 mole) and the synthesized temperatures (65, 75 and 85 °C). ZnO nanoparticles exhibited a high degree crystallinity with wurtzite hexagonal structure for all conditions carried out using SEM, XRD, EDS and Raman. It was clearly observed that both sodium hydroxide solution and synthesized temperatures strongly affected on the size and shape of ZnO nanoparticles. The smallest ZnO nanoparticle was observed to be 47 nm with 0.7 mole of sodium hydroxide solution at 75 °C. Uniformed ZnO nanoparticles were obtained at synthesized temperatures above 65 °C. Optical properties of ZnO nanoparticles were also studied and carried out as absorbance spectra. In addition, optical energy band gap of ZnO nanoparticles was in the range of 3.24-3.35 eV.