This investigation was focused on properties of polyurethane (urea) (PUU) by incorporating silica sol-modified nano-calcium carbonate (CaCO3). The FT-IR spectroscopy and ? potential measurement indicated the presence of a hybrid effect due to the hydrogen bonding between the nano particles and the polymer matrix. For these hybrid aqueous dispersions, the particle size decreased as the modified nano-CaCO3 content increased, and the polydispersity index was very narrow (<1.20). Films prepared with the hybrid PUU aqueous dispersions exhibited excellent waterproof performance: the amount of water absorption was as low as 9.0 wt %, and the contact angle of water on the surface of this kind of film was as high as 93 degrees C. TGA results indicated the high thermal stability of hybrid PUU polymers (223-255 degrees C). The properties like tensile strength, hardness, and elongation at break were influenced by the modified nano-CaCO3 content in the polymers. The hybrid PUU with 15 wt % modified nano-CaCO3 content showed the optimum properties. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012