CaSO4 center dot 2H(2)O was converted to alpha-CaSO4 center dot 0.5H(2)O at 92 degrees C in the wet-process phosphoric acid pulp (28% by mass) in the presence of phosphogypsum and alpha-CaSO4 center dot 0.5H(2)O nuclei (up to 40%) in periodic (up to 180 mm) and continuous processes. Three sources of H3PO4 and phospho gypsum were taken into consideration (phosphorites from Togo, Syria and Egypt). The conversion degree was 85-89% depending on the reaction time and H3PO4 origin. A conversion of phospho gypsum was also obsd.