This work studies how nanosilica particles interact with a commercial dispersion of non-functionalized carbon nanotubes rich in surfactant and how this combination affects the pozzolanic activity of the nanosilica in a cement paste.The materials used were multi walled carbon nanotubes (MWCNT) dispersed in water with an anionic surfactant as dispersing agent, colloidal silica nanoparticles (NS) dispersed in water, and Class G cement.Cement pastes with a water-to-cement ratio of 0.45 and additions of MWCNT and NS up to 0.50% by mass of cement were produced in two steps;the dispersions of nanoparticles were combined with the mixing water using an ultrasonic tip processor, and then the cement was added and hand mixed until a homogeneous paste was obtained.