In the injection- and compression-molded specimens composed of isotactic polypropylene (iPP) and poly(ethylene-co-octene) rubber (EOR) blend, its morphological changes with temperature variation were investigated using an atomic force microscopy equipped with a heater accessory. Phase-separated sea-island structures comprising the iPP matrix (sea) and the EOR domains (island) were clearly observed in both specimens. In the injection-molded specimen, the morphology of the EOR domains was fibrous along flow direction (FD). In the iPP matrix, a stripe-like structure consisting of alternating iPP crystalline lamellae and amorphous region was clearly observed at room temperature. As increasing temperatures, the iPP amorphous regions seemed to shrink gradually and could not be identified at 80 degrees C. By contrast, in the compression-molded specimen, the EOR domains were circular in shape, and the alternate structure comprising the iPP crystal lamellae and amorphous regions was also found. At elevated temperatures, the iPP amorphous regions gradually enlarged. The analysis of the apparent activation energy obtained by a dynamic mechanical thermal analysis revealed that the differences in the morphological behavior in the iPP matrix region between the both specimens were attributed to the differences in the mobility in the iPP crystal regions. (c) 2008 Wiley Periodicals, Inc.