The behaviour of the blended cements, containing  limestone filler in corrosive environments is an important aspect for assesing the durability of concrete prepared with such cements having a diminished „clinker factor”. Such cements are of great interest from economic and environmental point of view. The present paper provides information regarding the behaviour of blended cements, with 10-40% limestone filler (Blaine specific surface area of 4600 cm²/g and 7000 cm²/g respectively), immersed into 5% MgSO₄ solution, from 28 to 580 days. X-ray diffraction (XRD) and scanning electron microscopy (SEM+EDAX) data allow the formulation of some possible interactions that occur between the binding matrix and sulphate solution. As a result of such reactions some hydrates as gypsum, ettringite, brucite are formed. Corrosive processes are carried out progressively from the surface towards the inside of the samples, which involve compositional and structural differences between the two areas. The corrosive effect of MgSO₄ solution is highlighted by the decreasing  in mechanical strength of the mortar samples for long period of exposure, up to 580 days.  The behavior of mortars in magnesium sulfate solution seems to be positively influenced by using finer limestone filler (Blaine specific surface area of 7000 cm²/g), due to a higher compactness for samples.