Structure and biocompatibility are key parameters that determine the usefulness of dental materials for clinical use. Novel polyurethane (PU) nanocomposite material was prepared by chemically binding nanohydroxyapatite (nHA) to the diisocyanate component of the PU backbone by solvent-polymerization. nHA was incorporated into PU by the stepwise addition of monomeric units of the PU. The PU/nHA composite was analyzed by 13C Nuclear magnetic resonance (structural) and X-ray diffraction (phase analysis). The tensile strength and elastic modulus was evaluated for mechanical properties. These analyses revealed linkage between the hard- and soft-segments are urethane linkage and showed high mechanical properties with increase in content of nHA. To assess biocompatibility osteoblast cells were seeded on to the material and allowed to adhere and proliferate. Osteoblast-like cell growth and proliferation was assessed by MTS assay. It was found that cells adhered and proliferated on these novel substrates. To test bacterial adhesion discs of composite with and without nHA were incubated with standardized suspensions of oral bacterium Streptococcus sanguinis strain NCTC 7863. PU composites with nHA exhibited biocompatibility with respect to mammalian cell growth and showed significantly reduced bacterial adhesion as compared to PU alone. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012