High performance mortars were either microwave-treated, at 80°C for 15-780 min, or wet-cured, at 80°C for 24h, and their mechanical properties (flexural and compression strength) and microstructural features (porosity, bound water, texture of crystalline components) investigated. The cement was a type I 52.5 OPC to which microsilica was added as the pore filling component. The aggregate was natural sand. A low water to cement ratio (0.24) and a polymeric acrylic superfluidifier were used to limit the residual porosity and retain good workability. The compressive strength, after 24 h at room temperature, was ~50 MPa which increased to ~100 MPa after hot wet cure (flexural data were ~6 and ~16 MPa, respectively). For the microwave treated mortars the compressive strength varied from ~50 to ~110 MPa, depending on the duration of exposure and sample confinement during the treatment. The strength of mortars was strictly related to the variation of water content. Both the total porosity, evaluated by mercury intrusion porosimetry, and the threshold pore size, regularly decreased on extending the microwave treatment. X-ray diffraction spectra showed that the cement constituents did not react completely due to the limited amount of water and the brevity of the treatment. The cement gel of microwaved mortars appeared to be better structured than that of the wet-cured counterpart.