Organic phase change materials (PCMs) have been widely used in the thermal energy storage field, but melt leakage above the phase change temperature has greatly hindered their practical applications. Herein, poly(vinyl alcohol) (PVA) aerogels with hierarchically porous structure are fabricated and introduced into phase change matrices to obtain novel leakage-proof composite PCMs (CPCMs). The thermal storage efficiency of the working substance in the CPCMs reaches as high as 95.6%, maintaining a tremendously high energy storage density. More importantly, the CPCMs exhibit prominent shape stability when heated at 80 degrees C, higher than the phase change temperature, for 60 h. Finally, the leakage-proof CPCMs exhibit great application potential in the thermal management of electronic devices.