Synthesis of nano-CaCO3 (nano-calcite) was carried out using sonochemical carbonization. CO2 gas was used for carbonization of Ca(OH)(2). The effect of sonicator probe size (10, 14, and 20 mm diameter) on synthesis process was Studied for constant ultrasonic power. Further, CO2 gas was passed through sonicator probe drilled with hole along the length to investigate the effect on synthesis mechanism. The synthesis processes with and without ultrasound were compared. Similar comparison was done for synthesis, where ultrasonic probe used was with and without holes. The results showed that the application of ultrasound into the synthesis causes a super-saturation of Ca2+ ions in the synthesis leading to a rapid nucleation of CaCO3 and improves the solute transfer rate. XRD gram shows that the nano-CaCO3 obtained under sonication process gives the particle size of 35-50 nm, while without ultrasound it is 104 nm. Higher the probe size, there is a decrease in the particle size. The innovative arrangement of passing the gas through the probe instead of the separate sparger tube gives a reduction in the particle size. The preferred orientation of XRD peak for nano-CaCO3 is observed to change from (10 10) plane to (1 19) plane in case of 20 and 14 mm probe diameter with hole. (c) 2008 Elsevier B.V. All rights reserved.