External Sulphate Attack on sulphate-resisting Portland cement concretes is a well-researched field. However, the effect of temperature on the performance of sulphate attack requires further attention. For this purpose, cubic mortars were made with sulphate resisting Portland cement (low C(3)A) and two types of sand, silica and limestone, which were then immersed in a 5% MgSO4 solution at different temperatures: 5, 20 and 50 degrees C, for 24 months. The deterioration of mortars due to magnesium sulphate attack was evaluated by measuring changes in mass, compressive strength, porosity and sorptivity. The X-ray diffraction was also used to determine the different mineral phases, and the pH of the conservation solutions was monitored. No damage was observed on the samples exposed at 50 degrees C. However, serious damage was noted on mortars made with silica sand exposed at 5 degrees C. Results show that high temperature improved some physical and mechanical properties and do not necessarily accelerate the degradation due to magnesium sulphate attack. Sulphate-resisting Portland cements with limited C(3)A content was found to be susceptible to Thaumasite Sulphate Attack. The type of sand has a remarkable effect on the performance of mortars at low temperature compared to high temperature. The samples with limestone sand showed better resistance against magnesium sulphate attacks.