Abstract: For thermal energy storage application, polyurea microcapsules about 2.5 μm in diameter containing phase change material were prepared using interfacial polycondensation method. In the system droplets in microns are first formed by emulsifying an organic phase consisting of a core material (n-hexadecane) and an oil-soluble reactive monomer, toluene-2,4-diisocyanate (TDI),in an aqueous phase. By adding water-soluble reactive monomer, diamine, monomers TDI and diamine react with each other at the interface of micelles to become a shell. Ethylenediamine (EDA), 1,6-hexane diamine (HDA) and their mixture were employed as water-soluble reactive monomers. The effects of diamine type on chemical structure and thermal properties of the microcapsules were investigated by FT-IR and thermal analysis respectively. The infrared spectra indicate that polyurea microcapsules have been successfully synthesized; all the TG thermographs show microcapsules containing n-hexadecane can sustain high temperature about 300 ℃ without broken and the DSC measurements display that all samples possess a moderate heat of phase transition； thermal cyclic tests show that the encapsulated paraffin kept its energy storage capacity even after 50 cycles of operation. The results obtained from experiments show that the encapsulated n-hexadecane possesses a od potential as a thermal energy storage material.