In the present study High Strength Concrete of M60 grade was designed by using Cement, Fly ash, Fine Aggregate, Coarse Aggregate, Water and Super Plasticizer following IS 10262-2009 and IS 456-2000. In the above mix cement was replaced partially with Nano Silica by varying percentages by weight (1%, 2%, 3% and 4%) and the effect of nano silica on the strength behaviour was studies. The Compressive, Flexural and Tensile strengths of the concrete were determined at 7, 14, 28 and 56 days and the results were compared.