The lamellar morphology of a melt-miscible blend consisting of poly(trimethylene terephthalate) (PTT) and poly(ether imide) (PEI) prepared by solution precipitation has been investigated by means of optical polarized microscopy (POM) and small angle X-ray scattering (SAXS). From the observation under POM, it was suggested that PEI was predominantly segregated into the interlamellar and/or interfibrillar regions upon PTT crystallization since the PTT spherulitic morphologies of blends were volume-filling. From results of SAXS data analysis, a larger amorphous layer thickness was identified in the blends, showing that some PEI was incorporated inside the interlamellar regions after crystallization. Despite the swelling of the amorphous layer, the amorphous layer thickness was relatively independent of the blend composition. It was concluded that amorphous PEI was located in the interlamellar regions of PTT as the weight fraction of PEI (wPEI) [<=] 0.1, while amorphous PEI was predominantly segregated into the interfibrillar regions of PTT as w(PEI) > 0.1, and the extent of interfibrillar segregation increased with increasing w(PEI). (c) 2005 Wiley Periodicals, Inc.