Abstract. The present work reports the results of an experimental campaign started two years ago and still ongoing, aimed to assess the behavior of different cementitious materials subject to external sulfate attack. To this purpose prismatic specimens of cement paste and specimens of mortar and concrete produced with the same Portland cement, were immersed in demineralized water and in different solutions containing 5% and 10% sodium sulfates. The expansion was monitored in time by direct length measurements and the degradation of the stiffness was indirectly obtained through non-destructive ultrasound wave propagation tests. XRD tests and SEM observations evidenced the presence of secondary gypsum in the outer part of the specimens were sulfates penetrated. An increase of the material porosity was also measured in this region.