During the heating of SrSO4 a structural change occurs at 1413 K. This structural change has effect on the thermodynamic and kinetic properties of the reduction process of SrSO4 to SrSO3. The structural change of the SrSO4 has not been reported in the literature, hence, it was decided to determine the heat of transformation of this phenomena, using the differential thermal analysis technique. It was found that this structural change also occurs in the sulfates of the alkali-earth metals. In the case of the sulfates of Mg, Ca and Ba, there are not reports of transformation heat data; the literature only reports the temperature at which the transformation takes place. In this work, the heats of transformation of MgSO4, CaSO4 and BaSO4 were also determined.