This paper describes a study undertaken to determine the influence of variation in cement content on the mechanical properties and durability of nano silica concrete. A series of tests such as chloride diffusion tests and conventional scanning electron microscopy (SEM) techniques are used to study micro structural features of concrete specimens contained nano particle of 1.5 percent of weight of cement. Furthermore, compressive strength of specimens was also investigated. As the cement content has significant effect on the properties of concrete, the cement content is varied and test specimens are examined for nano silica concrete mixture with cement content of 350, 400 and 450 kg/m(3) respectively. Test results indicate difference manner for nano specimen from those expected. Increasing cement content, the compressive strength of nano specimens (like water absorption) increase to an optimal value; while chloride diffusion index reduces faster than reference specimens. SEM observation shown that nano silica particles make the microstructure denser, on the other hand it produces more internal micro crack compare with reference concrete. Although high pozolanic activity of nano silica improves the microstructure of the concrete, these speed up hydration and cause large pores area around the anhydrate cement particles.