The impact of silica-nano-particles (SNP) on the hydration characteristics of composite cement containing flyash (FA) and/or fine granulated slag (FGS) was investigated. The physico-chemical characteristics of different composite-pastes are studied in the presence of 4mass% SNP and 40% FA and/or FGS with the existence of 1mass% polycarboxylate superplasticizer (SP). The physicomechanical characteristics are studied by determination of the consistency, setting times (STs), compressive strength (CS), total porosity, (TP), bulk density (BD), chemically combined water (Wn), free lime (FL) contents and gel/space ratio (X). The phase composition of the formed hydrates is investigated using XRD, DTA∕TGA, and SEM techniques. The represented data shown that 4% SNP improve the hydration process of the composite cement pastes and exhibit superior-compressive strength than neat-cement without SNP, this is due to nano-sized-particles and higher-efficiency of good pozzolanic-action of SNP in the comparison with FA and FGS. The composite cement containing OPC–40%FGS–4%NS in presence of 1%SP possess the highest improvement of mechanical-properties, hydration-kinetics, and microstructure of hardened cement pastes.