Abstract : The aim of the work is to study microstructural evolution of cementitious materials during hydration process and to analyse modifications due to drying effect. Two durability parameters are studied: water content and porosity. An original way for the investigation is to use Magnetic Resonance Imaging MRI. First, we present a bibliographic synthesis for cementitious materials and for MRI applied on porous media to analyse proton density linked to water content and relaxation NMR which gives information of pore size distribution. Then, results obtained with relaxation and MRI, are compared and identified with common destructive methods commonly used in civil engineering. Finally we analyze two important phenomena on cementitious materials: hydration process and hydration coupled to drying.