In this paper, a water based suspension containing microencapsulated phase change material (MEPCM) and multi-walled carbon nanotubes (MWCNTs) was prepared as a novel heat transfer fluid. Thermal and rheological properties of the sample were obtained experimentally from differential scanning calorimeter (DSC), thermal gravimetric analysis (TGA), thermal conductivity meter and rheometer. It is found that the addition of MWCNTs into microencapsulated phase change material slurry can effectively improve the thermal conductivity of the suspensions and it is also found that a blend of 10 wt. % MEPCMs and 1 wt. % MWCNTs suspension can achieve an optimal thermal performance and stability. (C) 2013 Elsevier Ltd. All rights reserved.