Microencapsulated phase change materials (PCM) must not experience any supercooling, otherwise cannot be used in any latent heat applications. In this study Rubitherm (R) RT58 and1-octadecanol were selected as nucleating agents in an attempt to reduce or eliminate the supercooling issue of PCM in microcapsules. The PCM microcapsules (PCMMC) were prepared using a suspension polymerization. Fourier transformed infrared (FT-IR) measurements confirmed that RT21 has been successfully encapsulated. Differential Scanning Calorimetry (DSC) shows that the onset crystallization temperature of PCMMC was approximately 10 degrees C lower than that of the non-encapsulated RT21, due to supercooling. The degree of supercooling has been reduced dramatically when either RT58 or 1-octadecanol was used. However, the addition of 1-octadecanol has a negative impact on the PCM thermal behaviour, which represented by spreading the solidification over wider range of temperature. PCM content in the microcapsule was determined using Thermal Gravimetric Analysis (TGA) and DSC measurements. TGA provided more accurate measure of the core material mass content, since the DSC measurement assume no change in the latent heat of the PCM due to the addition nucleating agent, which may not be true. SEM shows that the surface morphology of the PCMMC without a nucleating agent is a smooth. However, buckles and dimples were observed on the surface of the PCMMC when nucleating agent was introduced. The mass loss, when the capsules were place at 50 degrees C in oven, was higher and more significant when 1-octadecanol was added as a nucleating agent. In contrast, when Rubitherm (R) RT58 was used, the mass loss of the PCMMC was small and stabilized after a short period of time. The latent heat of fusion and phase transition temperatures of PCMMC containing 5 wt. % RT58 were stable even after 2000 thermal recycle. (C) 2015 Elsevier Ltd. All rights reserved.