Inorganic/organic ternary hybrid films that are constituted of gelatin (G), poly(monomethyl itaconate) (PMMI) and silica (Si0(2)), are used as a solid matrix to study the crystalization of calcium carbonate (CaC0(3)). These films are transparent and stable in aqueous solutions due to the formation of interpenetrated networks. In these films it is possible to modulate the concentration of the different functional groups and the flexibility of the film structure by changing the composition. These changes in composition affected the morphology of the CaC0(3) crystals and the polymorph obtained on the films. Depending on the film compositions, fried-egg-like or spherical calcite particles were observed on the films. Films of a specific composition induced the nucleation of vaterite, the less stable polymorph of calcium carbonate