The aim of this research is the preparation of a novel form-stable composite PCM by incorporation of capric acid (CA) within the expanded perlite (EP), characterization of the composite by SEM and FT-IR technique and determination of thermal properties and thermal reliability of the composite PCM using DSC analysis. The maximum proportion of CA as phase change material (PCM) in the composite was found as 55 wt%. This composite was specified as form-stable because it does not allow the melted PCM leakage even when it is heated over the melting point of CA. Thermal properties of the form-stable CA/EP composite PCM were measured using DSC analysis. Thermal reliability of the composite PCM was investigated by thermal cycling test with respect to the changes in its thermal properties. Thermal conductivity of the composite PCM was also increased approximately as 64% by adding 10 wt% expanded graphite. (C) 2007 Elsevier B.V. All rights reserved.