ZnO in different nanostructures were synthesized by microwave assisted hydrothermal route. Different experimental conditions such as microwave irradiation power, exposure time have been investigated to reveal the process of formation of the ZnO nanostructures. It was revealed that the microwave exposure time plays a vital role in determining the diameter of the rods. The interaction of microwaves with the growth units of ZnO was systematically investigated to explain formation of different structural geometry of ZnO on nanoscale. ZnO nanostructures consisted of flower-like, sword-like, needle-like and rods-like structures were prepared by microwave assisted hydrothermal process at different conditions of microwave power and irradiation time. The ZnO nanostructures are in hexagonal phase. It is considered that microwave can interact with growth units of ZnO to generate active centers on the surface of ZnO nuclei so that needle-like ZnO rods are created on those sites, resulting in the formation of the flower-like ZnO nanostructures. Polyaniline - ZnO nanocomposites (PZ) in various weight % of nanostructure ZnO were synthesized by the chemical oxidation method in sulphuric acid medium using ammonium persulphate as oxidant at 276K. The synthesized polymer nanocomposites were characterized by XRD, FTIR and UV-VIS spectroscopy.