Active pozzolacic admixtures, such as silica fume (SF) and metakaolin, are used in modern concrete technology to obtain high performance properties. Nano-scale pozzolans helps to achieve more dense microstructural packing and more impermeable cement matrix. Nanosilica (NS) was synthesised in laboratory by Sol-gel method and added to cement/SF paste in amount 2 wt.% from cement. Sol-gel nanosilica are characterised by very high specific surface (>30 m2/g). Thermal effect during cement paste hardening was investigated. Compressive strength and water absorption were tested for hardened cement paste (HCP) samples. Formation of microstructure was investigated using the method Fourier transmission infrared spectroscopy (FTIS). It may be concluded that adding Sol-gel nanosilica to cement/SF composition doesn’t give a considerable effect on final physical and mechanical properties of HCP, but significant effects on hardening processes in the initial stage of hydrating took place. The best intensification effect of hardening process refers to mix containing Sol-gel nanosilica calcined at 400 °C.