Blends of poly(styrene)-block-poly(ethene-co-but-1-ene)-block-poly(styrene) (SEBS) with isotactic polypropylene (i-PP) and with atactic polypropylene (a-PP) were prepared under different thermal treatments. On the basis of the phase imaging of tapping-mode atomic force microscopy (TMAFM), we investigated the nanostructures and the morphologies of these blends as well as their dependence on blending history. The observed macrophase separation in i-PP/SEBS blends is caused by the incompatibility of the two polymer components. The microphase separation of the SEES component depends on the thermal treatment. The morphology of a-PP/SEBS blends exhibits domains that span a wide range of sizes from 15 mu m down to 15 nm. Our work shows that TMAFM phase imaging is an important and competitive tool for studying the microphase separation of polymers.