Abstract: The purification of the raw phosphogypsum issued from the fabrication of phosphoric acid by reaction between phosphate rock and sulphuric acid consists of removing the extreme grain size fractions therefrom.This method has been developed after it has been found that a large part of the undesirable impurities are concentrated in the extreme grain fractions which constitute only a small percentage of the phosphogypsum. The impurities thus removed are P.sub.2 O.sub.5, F, SiO.sub.2, C, F.sub.2 O.sub.3 and Al.sub.2 O.sub.3.Purification efficiencies can be obtained of the order of 70 % for the total P.sub.2 O.sub.5 and fluorine, 60 % for silica, and 80 % for organic carbon, while water-soluble P.sub.2 O.sub.5 is substantially completely removed.