The polymorphism of calcium carbonate crystal was studied by introducing CO2 gas through a gas sparger or a double-tube gas injection nozzle into a pH-stat crystallizer containing calcium chloride solution. Several operating variables were investigated and the pH of solution and calcium ion concentration were the important factors that affect the formation of polymorphs of calcium carbonate. At ambient temperature either calcite or vaterite was the major product, depending on the pH and calcium ion concentration. Then the same crystallization system was employed to study the growth kinetics of calcite crystals, using a double-tube gas injection nozzle instead of a gas sparger, which cannot be used to suppress nucleation, to introduce the CO2 gas into the crystallizer. The growth rates of calcite seeds increased with increasing supersaturation ana crystal size. As a conclusion, the polymorphs and growth rate of calcium carbonate are controllable in a gas-liquid-solid reactive crystallizer, using a pH-statoperation mode.