Phase-change nanocapsule particles are successfully synthesized by the two-step miniemulsion polymerization method. Urea-formaldehyde resin is used as the shell material. Hexadecane is used as the core material. The particle size distribution and the surface morphology of nanocapsules are characterized by laser particle size analyzer, optical and scanning electron microscopy. The thermal properties are investigated by differential scanning calorimeter. The effects of the amounts of surfactant (AS) on the properties of prepared nanocapsules are also investigated. The results indicated that the nanocapsules have smooth surface and the mean particle size is about 270 nm; nano-structure of capsules has not changed dramatically after being heated at 100 A degrees C for 72 h; The phase-change enthalpy of nanocapsules increases from 114.6 to 143.7 J/g with the increasing of the AS, but the mean particle diameter decreases from 285 to 253 nm; The degree of undercooling of hexadecane decreases about average 94% after being encapsulated in capsules.