Monodispersed calcium carbonate spherical particles with a size of about 1-2 mum could be prepared by a precipitation reaction of sodium carbonate with calcium chloride in the presence of polymaleicanhydride (PMA) or poly (sodium 4-styene-sulfonate) (PSSS) at room temperature. The as-prepared products were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). It was found that the acidity of organic macromolecules is an important parameter for the formation of monodispersed CaCO3 microspheres, the stronger the acidity of organic macromolecules, the greater the adsorption ability to Ca2+ ions, the easier the formation of spherical particles and the smaller the size of microspheres. (C) 2004 Elsevier B.V. All rights reserved.