A kind of novel nanoencapsulated PCM with polystyrene as the shell and n-octadecane as the core was synthesized by the ultrasonic-assistant miniemulsion in-situ polymerization, and its morphology, structure and thermal properties were characterized by TEM, MIR, XRD, DSC and TG. The nanocapsules were regular spherical and ranged from 100 nm to 123 nm in size. All the characteristic peaks of n-octadecane and styrene were observed in the MIR spectrum of the nanoencapsulated PCM. The XRD result suggested that n-octadecane was encapsulated by the shell of polystyrene. The phase change temperature of the nanoencapsulated PCM was very closer to that of n-octadecane, and its latent heat was equivalent to that of the calculated value based on the mass ratio of n-octadecane measured by TG. (c) 2008 Elsevier Ltd. All rights reserved.