In this article, we have examined the thermal behaviour of Moroccan phosphogypsum in the absence of additives. We have used very diversified techniques : thermogravimetric analysis (TGA), differential thermal analysis (DTA), infrared spectroscopy and X-ray diffraction. DTA has allowed us to point out several transformations, Moreover, TGA has shown that the dehydration can occur in one step, which confirms that the sample is not bihydrated. The infrared spectroscopy has allowed us to characterize the water molecules of crystallization and the sulphate grouping of phosphogypsum.