Micro-thermal analysis (micro-TA) is a new subsurface thermal analysis technology. The average of the DC signal is a function of the thermal conductivity, and the response to the AC modulation signal is a function of the thermal diffusivity of the subsurface. Using this technique, three images based on topography, thermal conductivity, and thermal diffusivity are obtained simultaneously. Specific areas and domains in these images can then be characterized by simply positioning the probe and performing a localized thermal analysis experiment. The technique has been used to study the phase separation process in a 50:50 (by weight) polystyrene (PS)-poly(vinyl methyl ether) (PVME) blend and natural rubber-nitrile rubber blends. For these polymer blends, considerable contrast between phases is obtained, based on thermal conductivity, whereas optical and electron microscopy would show them as being very similar. For example, it is difficult to image the morphology of natural and nitrile rubber blends by means of transmission electron microscopy, because of their similar chemical structures. Micro-TA gives an excellent image of the morphology of these natural-nitrile rubber blends. This opens a new way for rubber industries to study morphologies of rubber-rubber blends in general. In the 50:50 PS-PVME blend, annealed at 125 degreesC, spinodal decomposition occurred. With increasing time, the domain size and the glass transition temperature of PS-rich domains increased, indicating that the concentration of PVME in the PS-rich phases decreases. The results imply that micro-TA can be used to image the composition in the near-surface or surface regions in multicomponent materials, if the resolution is high enough.