This paper assesses the influence of nanosilica particles (in low dosages) under limited dispersal conditions on some properties of pastes and mortars made out of conventional cement (without the use of plasticizers). For this, characterisation of mixtures in fresh and hardened states were carried out through setting times, fluidity, early compressive strength and scanning electron microscopy tests. As results, flowability of the analysed mortars was higher when the silica nanoparticles were larger in size, and consequently lower flowability values were obtained for the smaller nanoparticles. It was not possible to determine an optimum content of nanoparticles since no significant increases in the early compressive strength of mortars were achieved. The obtained results in this research show that for mortars with water/cement ratio of .55 a minimum nanosize and a high amorphous content of silica particles are not sufficient to enhance mechanical strengths, but mainly a better dispersion in the cementitious matrices should be guaranteed using plasticizing admixtures in order to optimise workability and mechanical performance.