We have used the sonochemical approach to synthesize single crystals CaCO3 nanocrystals with various anisotropic shapes of such as, nanowires, nanosheets and unusually obtained nanoplates without using any template at room temperature. The complex interplay between crystallization processes and self-assembly resulting from spatial constrains has been investigated through studying the structural evolution of metastable intermediates synthesized. The impurity inducing crystallization has been proposed for a reasonable understanding of the novel crystallization pathway under the condition of sonication. Moreover, this approach is suitable to the anisotropic single crystals synthesis of other alkaline earth carbonates such as SrCO3 and BaCO3. It also gives a new demonstration of sonochemical effects on the crystallization and assembly of block building in the mesoscale.