A composite material is made by combining two or more materials to give an unique combination of properties. Composites based on a polymer matrix have become more common and are widely used in many industries due to the advantageous properties offered by the polymers. Filling polymers with mineral dispersion has long been a practice in the plastic industry as a way to reduce overall production costs and enhance certain properties. Polymer Matrix Composites were prepared by blending vinyl ester resin with silane surface treated ZnO nanoparticles of various weight percentages. They were characterized by Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and TGA-DTA. Measurement of mechanical properties like Tensile strength, impact strength, flexural Strength, hardness and physical properties like water absorption, density, specific gravity, etc. have been carried out. The effect of particle size, particle distribution on mechanical properties, thermal properties and physical properties has also been studied. The changes in the properties of the composites with and without coupling agent have been compared. The results of the studies reveal that surface treated composites found to have nice improvement in overall properties than the untreated one.