The aim of this study is to investigate the effect of carbon-based materials on the thermal performance of microencapsulated phase-change material (µPCM) for passive cooling applications. The sample was prepared by mixing 5 wt. % of multiwalled carbon nanotubes (MWCNT) into µPCM using a powder metallurgy technique. The mixed powder was then compacted into a disc, having a diameter of 30 mm and a height of 5 mm, using a hot compaction technique. The samples were tested according to the modified ASTM standard. The experimental results demonstrated that the addition of MWCNT into µPCM enabled it to effectively absorb the heat emitted by the aluminium casing compared to pure µPCM. The model results indicated that the temperature of the aluminium could be maintained well at each ambient temperature by using the µPCM/MWCNT composite, thus showing that µPCM/MWCNT can potentially be used for passive thermal management in the future.