The spherulitic growth of poly(ethylene oxide) (PEO) was found to continue in the spherulites of poly(butylene adipate-co-butylene succinate) (PBAS) in the simultaneous spherulitic growth process of the two components in PBAS/PEO blends. This phenomenon, namely the formation of interpenetrating spherulites (IPS), was analyzed on the basis of birefringence observed by polarizing optical microscopy. The growth direction of PEO lamellae in the PBAS spherulites was found to be along the preexisting PBAS lamellae. PEO crystals also nucleated inside PBAS spherulites and showed spherulitic growth in them at relatively high crystallization temperatures. The conditions for realizing IPS were also discussed. Miscibility in these novel crystalline/crystalline polymer blends in the molten state was confirmed by differential scanning calorimetry and optical microscopy. © 2005 American Chemical Society.