Abstract: The functionally thermal fluids made by suspending fine phase change material (PCM) particles (dispersion phase) in a carrier fluid (continuum phase) have spontaneously flowability and large heat (or cold) storage. Some complex or nonlinear physical phenomena both in heat transfer and fluid flow are displayed. The natural convection characteristics of this kind of fluids are summarized，including heat transfer enhancement，stability，effects of particle size and some thermophysical properties. The future research on utilizing this kind of fluids was also discussed.