In this investigation, chitosan membranes with different surface average degrees of deacetylation (DA) are prepared and then are employed as the support matrix to culture calcium carbonate (CaCO 3 ). In the presence of high concentration of polyacrylic acid (PAA), the CaCO 3 films obtained on the surface of all chitosan films mainly consisted of vaterite, which suggests the presence of bulk PAA plays an overwhelming part in stabilizing the vaterite. As a comparison, the influences of active groups indicate that only in case of low concentration PAA the thin CaCO 3 films grown on chitosan with 8% DA mainly consisted of vaterite owing to the strong nucleation ability of –NH 2 group, whereas, for those grown on chitosan with 80% DA the CaCO 3 films mainly consisted of aragonite. A more complex scenario revealed that in the case of intermediate concentration of PAA the formed polymorphs behave as mixtures of vaterite and aragonite.