Using a pH-stat apparatus, we produced crystals of calcium sulfite hemihydrate in a semibatch crystallizer by reacting Ca(OH) 2 with NaHSO 3 under various operational conditions. The habits of calcium sulfite hemihydrate obtained in this study were acicular, long-platelet, platelet and tabular. Each of them was prone to form agglomerates, depending on the pH value, solution composition and concentration of additives. At low pH and high concentration of sodium bisulfite the agglomerate of acicular crystal would form. In contrast, platelet and tabular crystals and their agglomerates were obtained at high pH and low levels of sodium bisulfite concentration. The particle morphology was not significantly altered by the addition of EDTA and DMA, but the crystal habit was tabular at low EDTA concentration and became platelet as the EDTA concentration increased.