Abstract: In-situ modification method was adopted to prepare hydrophobic CaCO<SUB>3</SUB>,.e.hydrophobic CaCO<SUB>3</SUB> particles were directly prepared via carbonation of Ca(OH)<SUB>2</SUB>in present of modifier.The influences of the sorts of modifier,ime of adding modifier and dosage of modifier on modification effect were studied.The results indicated that the modification effect of sodium stearate was relatively better;he measurement of activation grade indicated that the prepared CaCO<SUB>3</SUB> was hydrophobic;he activation grade of modified CaCO<SUB>3</SUB> can get to 97.1% when the dosage of sodium stearate was 3%(as CaCO<SUB>3</SUB>) at digestion.IR,TA analysis of product indicated the hydrophobicity was due to the C<SUB>17</SUB>H<SUB>35</SUB>COO-combined with Ca<SUP>2+</SUP>on surface of CaCO<SUB>3</SUB> to form insoluble calcium stearate，which covered on the surface of CaCO<SUB>3</SUB> and modified its surface property.<BR>