Nanocapsules used as phase change material (PCM) were prepared by using in situ polymerization methods. N-Tetradecane was used as the core material. Urea and formaldehyde were used for the shell polymerization. Sodium dodecyl sulfate was used as the emulsifier and resorcin was used as the system modifier. The morphology of the nanocapsules was observed by a scanning electronic microscope (SEM). The thermal properties were investigated by a differential scanning calorimeter (DSC) and a thermogravimetry analysis (TGA). The SEM analysis indicated that the nanocapsules had general size of about 100nm and the core material was well encapsulated. DSC analysis indicated that the mass content of n-tetradecane was up to 60%, which resulted in a high latent heat of fusion of 134.16 kJ/kg. TGA showed the thermal stability of the nanocapsules could be improved by the additives (NaCl) used in the polymerization. The nanocapsules could be applied for thermal energy storage and heat transfer enhancement. (C) 2009 Elsevier B.V. All rights reserved.