The practical use of organic phase change materials (PCMs) for solar thermal energy storage is limited by the leakage problem and the low thermal conductivity. As a good supporting and thermal conductive framework for organic PCM with shape-stability, three-dimensional carbon sponges are produced by the direct carbonization of low-cost and sustainable biomass cotton. The carbon sponges are consisted of aerogels of the cotton-derived hollow carbon fibers, which have both interconnecting network and high porosity. The vacuum impregnated paraffin@carbon sponge composites not only present leakage-proof shape stability and enhanced thermal conductivity, but also show high thermal storage energy density (> 200 J g(-1), slightly lower than the pure paraffin) and good cyclability. The results indicate that the shape-stable PCMs as supported by cotton-derived carbon sponges are potentially to be widely used for thermal energy conversion and storage, especially for solar energy utilization.