Applying nano technology has driven the enhancement of many materials, one of which is nano-silica (nS). Therefore, the effect of nano-silica was investigated in this research. 13 mixes were cast and cured for three different ages 3, 7, and 28 days. A compressive strength test was applied on 117 specimens and a slump test was recorded 13 times. The results indicated that the compressive strength increases as nano-silica content increases and the nano-silica serves as an activator to promote the process of hydration. However, the compressive strength was slowly developed when fly ash existed in the mix. The highest and lowest compressive strength values obtained for the concrete mixes were In mix 8 and mix1, respectively at all 3 different ages. Mix 8 contained 1% nano-silica and 5% silica fume, while mix 1 contained 0.25% nano-silica and 2% fly ash. Silica fume properties can react fast with water molecules, and This leads to a positive effect on compressive strength and other mechanical properties. The lowest slump value (46 mm) was for the highest percentage of nano-silica, fly ash, and silica fume for slump test results. Despite the presence of relatively large quantities of fine materials in all mixtures, this effect was not apparent in the early age of the specimens (3 days). It was most evident at the age of 7 and 28 days. Silica fume specimens had low variation at 7 days with 1% nano-silica. This is attributed to the highest percentage of nano-silica that can fill voids and react faster than silica fume particles then interrupting it. This experimental work recommends to use nano-silica with silica fume rather than fly ash. These two materials can provide the best compressive strength in a short time.