Cement mortar prisms were made with three  different cementitious materials (with or without mineral admixture) plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at different temperatures (5⁰C, 20⁰C and alternate temperature between 5⁰C and 20⁰C) for a year. The strength development was measured on these immersed prisms at intervals, and samples selected from the surface of prisms were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that the influence of temperature on the resistance to sulfate attack of mortar is related to the binder compositions. A higher temperature leads to a quicker strength loss of the mortar without mineral admixture. For blended cements, a higher temperature is favorable for the pozzolanic reaction of mineral admixture and the overall deterioration of mortar is reduced. After 1 year of exposure to magnesium sulfate solutions, the formation of thaumasite was checked in the OPC mortars at both 5⁰C and 20⁰C. It is concluded that the thaumasite formation is not limited to structures at low temperature (less than 15⁰C).