In this work phase change material Nanocomposite (nPCM) was prepared based on paraffin and copper oxide (CUO). CUO has been used to improve the thermal conductivity of paraffin. Since the final properties and efficiency of nPCM is dependent on dispersion of nano particles in matrix, the surface of CUO particles was treated by trimethoxy(octadecyl)silane. Grafting of Silane on the CUO surface was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermo gravimetric analysis (TGA) techniques. The effects of Nano particles on latent heat and thermal conductivity were measure by Differential scanning calorimetery (DSC) and KD2. According to the results, increasing the nano copper oxide in composite caused an increasing the thermal conductivity and decreasing the latent heat. Moreover, the results showed that time of solidification and melting process decreased.