The effects of the presence of a polyelectrolyte on the polymorphism and particle size and shape of calcium carbonate crystals during reactive crystallization were investigated. Crystals were created by the single-jet reaction crystallization method. When polyacrylic acid (PAA) was added, the polymorphism and particle size and shape were different for each molecular weight of PAA and each experimental method. When sodium carboxymethylcellulose was added, the polymorph became different from those made by adding PAA and the particle sizes and shapes were different for each concentration. As a result, it is suggested that the method to achieve supersaturation, such as type of feeding, feed rate, kinds of polyelectrolyte and their concentration, may affect the polymorphism and particle size and shape of calcium carbonate.