A new kind of nano composite phase change material (NCPCM) was prepared using sodium stearoyl lactylate (SSL) as a surfactant to improve the dispersion of the Al2O3 nano-particles (with 2.5, 5, 7.5, and 10 wt.%) in paraffin with a SSL/Al2O3 mass ratio of 1:3.5. To evaluate the efficiency of the prepared PCMs, the melting rate of them at a temperature range of 50-60 degrees C and the effective thermal conductivity values in the solid and liquid states at a temperature range of 25-75 degrees C were measured using the k-type thermocouple and the transient hot wire technique, respectively. The heat storage behavior of the samples was investigated and their melting temperature, latent heat, and thermal reliability were determined using differential scanning calorimetry (DSC). Results showed that effective thermal conductivity enhancement ratios for the sample containing 10.0 wt.% nano-Al2O3 were 31% and 13% in the solid and liquid states, respectively, which are higher than those reported in similar studies. In addition, melting rate increased by 27%. As expected, all the PCMs showed good thermal reliability after 120 melting/freezing cycles. Based on our results, it may be concluded that the prepared PCMs can be regarded as effective heat storage materials for application in energy storage systems. (C) 2015 Elsevier Ltd. All rights reserved.