Abstract: Aliphatic polyurethanes based on 4, 4′-dicyclohexylmethane diisocyanate ( H₁₂MDI), poly ( ethylene glycol) (PEG), castor oil (CO), 1, 4-butandiol (BDO) and bioactive nano-hydroxyapatite (n-HA) were selected to prepare a nanocomposite by the prepolymerization method. The mechanical and thermal properties of the nano-composites were investigated. The results show that the tensile strength and broken elongation of the nano-composites are all reinforced with the addition of nano HA particles. When incorporation of 30 wt% n-HA into PU matrix, the tensile st rength and broken elongation increase by 186 % and 107 % compared to those of pure PU, respectively, which reach the maximum values. The storage modulus of the composites increases obviously with the increase of n-HA loading. The nano composites exhibit improved thermal stability with the incorporation of HA nanoparticles, and the differential scanning calorimetry (DSC) indicates that the incorporation of n-HA can hinder the crystallization process of PU. These results suggest that the n-HA/PU composite might be a prospective material for future applications in tissue engineering.