Abstract: The rheological characteristics of suspensions ofmicroencapsulated phase change materials (MPCM) in the presence ofnano-particles are investigated experimentally. Such type of novelsuspensions is found to behave as Newtonian fluids under relevant conditions studied in this work. Temperature affects the viscosity of suspensions significantly,and viscosity of base liquid and that of suspensions change withtemperature in a similar fashion. It is also found that viscosity of thesuspensions increases in a nonlinear fashion with increasing concentrationof nano-particles. The increment of viscosity is about 23\% when the massconcentration of nano-particles is up to 5%.