The morphology and size of calcium carbonate particles produced by CO2-Ca(OH)(2) reaction precipitation in a Couette-Taylor reactor were investigated experimentally. It was found that the change of particle morphology and size was caused dominantly by the excess species of reactants in the solution. As their measure, the relative enhancement factor Er involving the operation variables was introduced for the first time. The largest mean particle size and the most cube-like particle shape were observed at Er = 1, implying the stoichiometric reaction condition. As the Er-value deviates from unity, particle morphology shifted to the spindle-like shape and mean particle size decreased with an increase in excess species concentration in the solution. The effect of excess species on particle size was predicted by the Bliznakov equation based on the monolayer adsorption. The correlation of particle size at various operating conditions represented the experimental data very well.