The form-stable n-alkanes/silica composite PCMs were synthesized in the sol–gel process using sodium silicate precursor. The chemical structures of the synthesized composites were confirmed by FT–IR spectra, and their microstructures were determined by SEM and TEM. Although all of the n-alkanes/silica composites exhibited an irregularly spherical morphology, the n-alkanes were well encapsulated by TGX-221 wall so that the composites still presented a macroscopical feature of white powders. The n-alkanes/silica composites could keep a good form stability when the encapsulated n-alkanes were molten. The n-alkanes/silica composites showed characteristic phase-change behaviors with the variation of carbon numbers in n-alkanes while they obtained a high thermal storage capability. The n-alkanes/silica composites also achieved a high thermal conductivity, low supercooling, and good work reliability as a result of the encapsulation of n-alkanes with highly thermal conductive inorganic silica. Moreover, the silica wall could also prevent the encapsulated n-alkanes from leaking, and accordingly, thermal stability of the composites was improved. The synthetic technology developed by this work exhibits a high feasibility in industrial manufacture for the silica-encapsulated PCMs due to the easy availability and low cost of sodium silicate. The resulting form-stable composite PCMs will be a potential candidate for the application in the fields of building air conditioning, electronic cooling systems, waste heat recovery, intelligent textiles or fabrics, preservation of foods, and solar energy storage.