A hydroxyapatite (HAp)-polyvinylalcohol (PVA) nanocomposite was prepared by the in-situ method. When the HAp was synthesized by reacting Ca(OH)2 with H3PO4 in the presence of PVA having carboxyl groups, the interaction between the carboxylic groups of PVA and calcium ions of HAp led to the formation of nanometer-sized spindle HAp particles (long axis ca. 80 nm and short axis ca. 25 nm). The reactant was stable and formed transparent thin films by the casting method. Nanometer-sized HAp particles were uniformly dispersed in PVA film. Properties of the HAp-PVA nanocomposite film, such as tensile strength, gas barrier, and pencil hardness, were superior to those of the pure PVA. Furthermore, the nanocomposite film had high ionic conductivity compared to pure PVA and traditional composite. The ionic conductivity of the stretched film (PVA: HAp = 1:1) with 35wt % content of LiN(CF3SO2)2 was about 10-3 S/m at room temperature. Regarding the mechanism of this study, we believe that the HAp particles play a crucial role in increasing the free lithium cations to accelerate the ionic conductivity, according to the ionic interaction on the HAp surface.