This paper investigates the effect of nano particles on the mechanical properties at different ages of concrete. Different mixtures have been studied including nano-silica (NS), nano-clay (NC) or both NS and NC together with different percentages. Mechanical properties have been investigated such as compressive and flexure strength through testing concrete prisms 40, 40 and 160 mm at 7, 28 and 90 days in order to explore the influence of these nano particles on the mechanical properties of concrete. Results of this study showed that nano particles can be very effective in improving mechanical properties of concrete, nano-silica is more effective than nano clay in mechanical properties and wet mix gives higher efficiency than dry mix. Exceeding a certain percentage of nano particles in concrete negatively affects the mechanical properties. Also, binary usage of nano particles; (NS + NC) had a remarkable improvement appearing in concrete compressive strength than using the same percentage of single type of nano particles. This improvement can be attributed to the reaction of nano materials with calcium hydroxide Ca(OH) 2 crystals, which are arrayed in the interfacial zone (ITZ) between hardened cement paste and aggregates, and produce C-S-H gel and the filling action of nano particles which cause more densified microstructure. A percent of 3% nano particles consisting of 25% NS and 75% NC gave the highest mechanical properties representing in both compressive and flexure strengths among other percentages. ª 2014 Production and hosting by Elsevier B.V. on behalf of Housing and Building National Research Center.