Abstract: A mathematical model is established to describe convective heat transfer in magnetic microencapsulated phase change material slurry (MMPCMS) flows in a circular tube under an external magnetic field. Influences of magnetic field strength, volume fraction of magnetic phase change materials (MMPCM), mass flow rate, and heat flux on convective heat transfer are analyzed. It shows that convective heat transfer of slurries is obviously enhanced by external magnetic field. Since distributions of MMPCM volume fraction and slurry temperature are changed clue to magnetic force on MMPCM.