Natural hydroxyapatite HAP, extracted from the animal bones was used as filler for carboxylated acrylonitrile-butadiene rubber XNBR. Physicochemical properties of the HAP were investigated. It demonstrated the tendency to create the structure in paraffin oil. When added to rubber, HAP formed a molecular filler network, which was observed from the dynamical mechanical analysis. Hydroxyapatite appeared to be active filler, since mechanical properties of the vulcanizates were improved upon filling. However, the dispersive component of the hydroxyapatite surface energy was slightly higher in comparison to the value which corresponds to the rubber.