An experimental study is presented on the cement mortar incorporated with expanded graphite (EG)/paraffin composite phase change material (PCM). The composite PCM was prepared by absorbing paraffin into EG with vacuum absorption method. The heat storage cement mortar (HSCM) with proper mass fraction of the composite PCM was prepared. A testing device was designed for evaluating the heat storage effect of HSCM. Temperature variation and heat storage coefficient of HSCM were compared to those of the ordinary cement mortar (OCM). For a cubic with one HSCM board and a cubic with one OCM board, the maximum indoor center temperature difference is 2.2 K during the heat storage and 1.5 K during the heat release process. The heat storage coefficient of HSCM board is 1.74 times of that of OCM board. The results indicate that the HSCM board has good heat storage property. (c) 2012 Elsevier Ltd. All rights reserved.