In this paper, an experimental investigation on the use of silica fume and amorphous Nano silica on compressive and tensile strength of HSC was done at different cement contents. The percent of Silica fume and Nano silica were 10% and 1% respectively. Three cement contents, namely, 500 kg/m³, 600 kg/m³ and 700 kg/m³were used. All tests were performed at 28 and 56 days. Silica fume and amorphous Nano-silica are used as partial replacement of cement. Further investigation was carried out by combined replacement of silica fume (10%) and Nano silica (1%) of cement in the same mix. Compressive and split tensile strength of these mixes were measured and compared with the control concrete specimens. The experimental test results showed that concrete prepared with (1%) nano silica showed a good comparable strength (either compressive or splitting tensile) than the other two concrete mixes of 10%silica fume or combined silica+nano concrete. The test results showed also that there is a decrease in ratio of tensile to compressive strength as cement content increased for both 10% silica fume concrete and 1% nano silica concrete due to the  more increase in compressive strength gain.