In this study, arachidic acid (AA)/graphite nanoplate (GNP) composite material is proposed as a novel phase change material (PCM). In order to examine the influence of GNP loading into the base material (AA), composite PCMs were prepared with three different fractions (0.5, 1.0 and 2.0 in wt%). The thermal, chemical and morphological characteristics of the samples were introduced in terms of differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X-ray diffraction analyses. Moreover, the thermal conductivity values of samples in the liquid state were measured by means of 3 method. It was found that, for GNP fractions of 0.5, 1, and 2 wt. %, the thermal conductivity of composite PCMs have been increased by 15, 30 and 43% in comparison to the pure AA. Results also revealed that the GNP loading into the pure AA led to a reduction in the degree of subcooling and a small diminution in the latent heat values. Considering the thermal cycling tests, it was also obtained that the proposed composite PCMs remained stable even at the highest GNP loading. Conduction-dominated inward solidification process was simulated for one-dimensional spherical computational domain. For this particular case, it was found that the increments of 15, 30 and 45% in thermal conductivity tend to increase the effectiveness by 3.5, 6.4 and 8.7%, respectively. Copyright (c) 2015 John Wiley & Sons, Ltd.