A novel strategy for preparing hydrate salt/expanded graphite (EG) composite phase change materials (PCMs) with large latent heat capacity and high thermal conductivity is explored, which involves modifying EG with a surfactant, compressing the modified EG into a block, and immersing the block into a melted hydrate salt. TritonX-100 is employed to modify EG for improving its hydrophilicity. The block fabricated from the modified EG exhibits larger adsorptive capacity for a MgCl2 center dot 6H(2)O-NH4Al(SO4)(2)center dot 12H(2)O eutectic as compared with that of the unmodified one. The obtained eutectic/modified EG composite block exhibits a melting temperature of 63.40 degrees C and a melting enthalpy of as high as 157.8 J/g. The thermal conductivity of the composite block is measured to 4.789 W/m.K, about 10 times that of the eutectic. The novel eutectic/modified EG composite block shows great potentials in solar utilization systems, and this work sheds light on the development of EG-based composite PCMs containing hydrate salts.