Transparent thin films of calcium-ion-incorporated polymer composites were synthesized with calcium carbonate (CaCO3) and polymers such as poly(acrylic acid) (PAA), poly(ethylene glycol) (PEG), and methylcellulose. The homogeneous distribution of Ca2+ in the composite films was observed because of the high concentration of COO- groups along the PAA backbone for the complexation of Ca2+ ions. The optical transparency of the composites depends on the weight percentages of the three polymers and the molar concentration of CaCO3 in the composites. Maximum transparency was obtained for a composite film with a PAA/CaCO3 ratio of 9:1. The results indicated that methylcellulose improved the film-forming capabilities and that PEG improved the transparency of the composites. All polymer complexes were characterized with X-ray diffraction, fourier transfer infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, dynamic mechanical analysis, and optical transparency measurements. (C) 2004 Wiley Periodicals, Inc.