Encapsulation of phase change materials (PCM) using a poly(methyl methacrylate) network-silica hybrid as the shell material has been developed. n-Octadecane melted at 28 degrees C was used as PCM. Based on the suspension polymerization process, the microcapsules were prepared Successfully by mixing and by the reaction of ethylene glycol dimethacrylate with precopolymer solution with tetraethoxysilane (TEOS), whose resultant microcapsules had higher latent heat (AH = 151 J/g) than those without TEOS (AH = 88.3 J/g). The average size of the PCM microcapsules was about 10 pm. The silica content, n-octadecane content, and latent heat of microcapsules were changed with varying ageing conditions, ageing time, and temperature. The highest amount of latent heat (Delta H = 178.9 J/g) and n-octadecane content (73.3%) of the microcapsule were obtained when the inorganic/organic ratio of the microcapsule was 5%. It was difficult to increase n-octadecane content (74% to 55.7-67.9%) and latent heat (180.5 J/g to 135.9-165.7 J/g) of the microcapsules by introducing different functional groups of coupling agents. 0 2009 Wile), Periodicals, Inc. J Appl Polym Sci 112: 1850-1857, 2009