This study is focused on the preparation and characterisation of n-nonadecane-vinyl copolymer shell nanocapsules for thermal energy storage medium. The n-nonadecane nanocapsules were prepared by a one-step miniemulsion in situ polymerisation method. n-Nonadecane was used as a core while styrene (St) and methylmethacrylate (MMA) was used as a vinyl copolymer shell. The Fourier transform infrared results confirmed that n-nonadecane nanocapsules were successfully synthesised. Morphological characteristic analysis indicates that these nnonadecane nanocapsules that were prepared using St/MMA (4:1) have a spherical shape and a narrow particle size distribution, with an average diameter of 160±11 nm. The maximum encapsulation ratio for n-nonadecane nanocapsules is 45.8 wt%. The DSC result of pure n-nonadecane and n-nonadecane nanocapsules exhibits two different peaks, which are related to their carbon numbers. The temperature and latent heat of melting and freezing of the n-nonadecane nanocapsules were determined to be 33.1 o C, 76.9 J/g and 30.2 o C, 82.0 J/g, respectively. Moreover, n-nonadecane nanocapsules exhibit good thermal and chemical stability, even after 1000 cycles of a thermal cycling test. Based on all of the results, it can be concluded that the n-nonadecane nanocapsules exhibit better energy storage and have good potential for buildings, textiles or other applications.