Monoclinic (alpha) and hexagonal (beta) polypropylene (alpha-and beta-PP) were stained in the vapor of a ruthenium tetroxide solution prepared in situ. The effect of staining on the fusion behavior was investigated using a DSC. A staining duration between 10 and 24 h was found suitable for obtaining a good electron contrast between the crystalline and amorphous regions for TEM examination without causing severe damage to the crystals. The spherulites of the water-quenched alpha-PP were found to be composed of very fine cross-hatched lamellae whose long period was about 10 nm. In comparison, the beta-PP spherulites crystallized isothermally at 130 degrees C had a category 2 morphology and the lamellae have a long period of 20 nm. The morphology of the spherulite boundary varied depending on the contact angle between the lamellae of the neighboring spherulites.