The effect of particle size in nanoscale on the biological activity, surface and electrical properties (surface area, electrical conductivity, dielectric constant and dielectric loss ) of zinc oxide has been investigated. The nano-crystalline zinc oxide was prepared using several different routes: soft methods and high – energy ball milling. The characterizations of as – prepared powders were investigated and the effect of the preparation methods on each of the shape of particle size as and its surface morphology was studied and discussed using different models. The use of the prepared zinc oxide nanoparticles was studied, i.e., in two applications as photo-catalytic material and solar energy .