The hydrothermal method has been used for the synthesis of ZnO nanoparticles with controlled morphology. In the present study, NaOH was used as a precipitating reagent, contributed to the formation of nanoplate morphology. Ultrafine particles, 50 nm in size, could be obtained. Compared with other methods, this technique avoids large concentration gradients and gives better control of the particle growth in chemical processing systems. As precipitation is carried out at a low concentration, agglomeration is reduced, while when the reactant concentration is high, a high particle number density results and agglomeration is observed.