In the present work, nano-calcium carbonate powder was prepared by micropore dispersion method with assistance of oleic acid as surfactant. CO2 gas was dispersed into the Ca(OH)(2)/H2O slurry via a glass micropore-plate with the diameter of micropore about 20 mu m. To investigate the effect of oleic acid on the size of CaCO3 particles, different amount of oleic acid was added in Ca(OH)(2)/H2O slurry at 5 degrees C and 25 degrees C, respectively. XRD patterns show that cubic calcite is the only crystalline phase in all cases. ZPA data and TEM photo indicate that the average particle size synthesized at 5 degrees C without oleic acid is of about 40 nm, slightly smaller than that of prepared at 25 degrees C, and that the dispersity of sample prepared at 5 degrees C is better than that of 25 degrees C. When oleic acid is added in both temperatures, the average particle size decreases a little. FT-IR spectra demonstrate that oleic acid interacts with Ca2+ and carbon-carbon double bond existed on the surface of particle. Consequently, two opposite roles of oleic acid during the process of preparation of nano-CaCO3 were proposed, namely preventing nanoparticles from growing during reaction and making nanoparticles reunite to a certain extent after reaction. (C) 2011 Elsevier B.V. All rights reserved.