The present work discusses the scaling effect on steady and unsteady thermal processes at mini/microscale that behave differently from the bulk case. Fast transient thermal processes could not be realized at bulk scale because of large thermal inertia and seldom have applications for practical use. However, due to the development of state-of-the-art technology, the miniaturization of device size makes it possible to utilize thermal responses due to the significantly reduced thermal inertia. For the steady case, the thermal effect varies with the boundary conditions and flow parameters because the relative importance of different forces changes with size at mini/microscale. Thus, the thermal phenomena are different from the conventional cases and vary with size.