Morphologies of polyethylene-ethylene/propylene/diene monomer (PE/EPDM) particles in 93/7 polypropylene (PP)/PE blends were investigated. SEM micrographs of KMnO4-etched cut surfaces and fracture surfaces of the blends revealed the existence of the "flake" structure. In the particles, crystalline PE formations with flake shape, which remain after etching, are called flakes. In addition to the PE-crystalline flakes, amorphous PE, located between PE crystalline lamellae and EPDM rubber, complement the flake structure. The flakes are usually linked with the PP matrix, as seen in the heptane-treated cut surfaces. These links, although observed with compatibilized samples, originate from the crystalline nature of PE particles, if no compatibilizer is added. Separately, the morphology of Royalene (consisting of high-density PE and EPDM rubber, used as a PP/PE compatibilizer) was investigated by low-voltage scanning TEM. The interaction of the components in the PE/EPDM blends can explain the formation of the flakes and toughening of the PP/PE blends. (C) 2003 Wiley Periodicals, Inc.