The spherulitic structure and morphology development of poly(ethylene succinate)/poly(ethylene oxide) (PES/PEO) blends with one-step crystallization behavior were observed by means of polarizing optical microscope. It was found that the pure PES spherulite in which the adequate quantity of PEO melt existed in the interlamellar regions

and the blending spherulite formed by both PES and PEO lamellae could form simultaneously. When the two types of spherulites contacted with each other the front of the blending spherulite could penetrate into the pure PES spherulite to grow continually. This penetration growth behavior was also observed when the mini-crystal particles of the PES component were formed at lower crystallization temperatures. The kinetics analysis showed that the penetration growth rate was faster than that in the original melt. It was evidenced that the increasing of growth rate and the formation of new growth site should be the typical characteristics of interpenetrated growth in binary crystalline polymer blends.