Hydrophobic CaCO3 composite particles were prepared via crystallization of CaCO3 with a sodium trisilanolate [(c-C5H9)(7)Si7O9(ONa)(3)] in methanol. The molar ratio of calcium ion to the sodium trisilanolate was varied from 0.1 to 0.5. FT-IR and TGA analysis of the obtained product indicated that the trisilanol was bound to the crystalline CaCO3. By changing the concentration of the trisilanol, composite particles with different shapes and polymorphism were obtained. Low concentration of the trisilanol gave stable vaterite crystals, the polymorph of which did not change when the composite was kept in water for more than 1 week. The contact angle of the modified vaterite was 62+/-4degrees. Dispersability of the composites in a polystyrene matrix was significantly improved compared with a bare CaCO3. We have succeeded in surface modification of particles with the hydrophobic trisilanolate.