Calcium carbonate crystal growth on a chitosan substrate was achieved using a supersaturated calcium carbonate solution. Heterogeneous nucleation of the calcium carbonate crystals was significantly influenced by the chitosan surface profile. Poly(acrylic acid) (MW = 2000, PAA2K) was chosen to modify chitosan surfaces in aqueous solution. The adsorption of PAA2K occurred on the chitosan film surface. The thicknesses of the adsorbed chitosan films were determined by ellipsometry. X-ray photoelectron spectroscopy (XPS) was used to determine the surface structure of the modified chitosan films. Calcium carbonate crystal sizes and morphology were observed under a polarized optical microscope and a scanning electron microscope (SEM). PAA2K promoted the heterogeneous nucleation of calcium carbonate crystals on the chitosan film and at the same time suppressed homogeneous nucleation in solution.