Abstract: The effects of adding Nano-Silica (NS) into self-compacting high volume fly ash mortar have been investigated. Five self-compacting mixtures with different NS percentage (0, 1, 2, 3 and 4%) were prepared, cast and tested for fresh properties and as well as for compressive strength, accessible porosity, Interfacial Transition Zone (ITZ) and drying shrinkage. NS addition up to 2% has been found to improve hardened paste properties. However, more then 2% of NS will lead to adverse effects.