Ultra thin hexagonal crystallites of nano aluminium trihydroxide (ATH) with 100-200 nm in particle size and 20-30 nm in thickness have been synthesized by carbonation of sodium aluminate (SA) solution in a rotating packed bed (RPB) reactor, followed by thermal hydrolysis. Due to the intensified absorption of CO2 under high gravity situations, SA solution was acidified rapidly at a fine scale, and thereby nano-scale gelatinous particles of ATH were precipitated from the supersaturated SA solution. This paper mainly discussed the factors of controlling carbonation process such as carbonation temperature, high gravity level, SA concentration, G/L ratio and terminal pH on the properties of precipitated ATH, which were characterized by TEM, XRD and BET. With carbonation temperature lowered to 30 degrees C, ATH size sharply reduced to below 200 nm. Higher gravity level and higher G/L favor the absorption of CO2, resulting in higher supersaturation degree of precursor with the lower pH for nucleation stage. But only when pH values were kept steady in the nucleation stage, the formed particles had a minimum size. In order to achieve ATH crystal phase, the final pH should be above 12.0. When SA concentration rose to 2.0 mol/L, the productivity of ATH achieved 75%. (c) 2006 Elsevier B.V. All rights reserved.