The aim of this work is to study the influence of carbon nanotubes in the cement matrix of high performance concrete (HPC) on flexural and compressive strength. This paper describes the samples preparation for the flexural and compression experimental tests. In order to understand the effect of carbon nanotubes in the cement matrix, a scanning electron microscope (SEM) analysis was carried out. It was reported after experimental tests that an improper dispersion of nanoparticles can have a negative influence on the mechanical properties. The dispersion of carbon nanotubes in the cement matrix is the most important aspect in order to attain the predicated influence on the mechanical properties.