This article presents investigations on the synthesis of nano-CaCO3 by the simultaneous absorption of CO2 and NH3 into CaCl2 solution in a rotating packed bed (RPB). The influence of the experimental parameters including the high gravity level, gas volumetric flow rate, liquid volumetric flow rate, and initial CaCl2 concentration on the particle size of CaCO3 were studied. Transmission Electron Microscope image of the as-prepared CaCO3 shows that the mean size of the nano-CaCO3 particles was about 50 nm with a particle size distribution (PSD) of 10 - 80 nm. X-ray Diffraction pattern demonstrates that the nano-CaCO3 has a calcite crystal structure.