Aragonite thin films of calcium carbonate are selectively formed on crystalline poly(vinyl alcohol) matrices in the presence of poly(acrylic acid) in CaCO3 solution. For thin film formation, this is the first example in which aragonite is formed selectively by cooperation of only synthetic organic macromolecules. In contrast, the addition of poly(glutamic acid) results in the formation of vaterite thin films on the crystalline poly(vinyl alcohol) matrices. These results show that crystalline poly(vinyl alcohol) matrices can be used to select the polymorph from aragonite and vaterite by changing the soluble additive.