In an effort to investigate the growth mechanism of nacre, a conventional vapor diffusion method for CaCO3 crystal precipitation was applied to in vitro growth of calcium carbonate on freshwater H. cumingii Lea shell. In a 10mM/L CaCl2 solution without any additives, aragonite deposit was obtained on the nacre surface, specifically at the edges of nacreous tablets. At the early stage of the deposition (up to 4 hr), the deposit did not take any specific form. After 12hr of deposition, the deposit exhibited faceted morphology characteristic of crystalline. Further increasing the deposition time resulted in the formation of well-faceted crystals of tower-like shape. Both Raman spectra and X-ray diffraction patterns showed that the deposit consists of aragonite polymorph of calcium carbonate.