Relaxation 1H-NMR was used to characterize the nanostructure of cementitious pastes, together with measurements of hydration and mechanical properties. The influence of cure parameters (hydration time and temperature) and composition parameters (water-to-cement ratio and silica and superplasticizer addition) was studied. In silica-free materials, the relaxationtime curve shows five characteristic times, T1,i, each of them being related to a given class of porosity, ranging from very small pores, at the inside of C-S-H nanocrystallites, to large, capillary pores. In silica-containing materials, there is an appearance of a supplementary signal, which is due to a pozzolanic reaction.