In our experiments, four kinds of amino acids, such as L-Cystine (L-CYS), L-Tyrosine (L-Tyr), DL-Aspartic Acid (DL-Asp), L-Lysine (L-Lys) and the mixed systems Of L-Tyr (or L-Lys)/Mg2+, were used as effective modifiers to mediate the crystallization of CaCO3. The obtained crystals were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). As the results have shown, calcite was formed in L-CYS system while both calcite and spherical vaterite with various morphologies were produced in the presence Of L-Tyr, DL-Asp, and L-Lys whose ability to induce the formation of vaterite was enhanced in turn. It indicated that amino acids played an important role in the process of crystal growth of CaCO3, the addition of Mg2+ was helpful for the formation of aragonite. The possible formation mechanism of CaCO3 produced in different amino acid aqueous solutions was discussed in the end. (c) 2005 Elsevier B.V. All rights reserved.