The microstructure morphology of the poly(trimethylene terephthalate) (PTT) and amorphous poly(ethylene terephthalate) (aPET) blends prepared by solution precipitation has been investigated by means of optical polarized microscopy (POM) and small angle X-ray scattering (SAXS). From the observation of POM, it was suggested that aPET was predominantly segregated into the interlamellar and/or interfibrillar regions upon PTT crystallization with the evidence that the PTT spherulitic morphologies of blends were volume filling. From results of SAXS data analysis, the maximum scattering peak (q(max)) of Lorentz-corrected SAXS profiles, amorphous layer thickness (I-a) and lamellar volume stacking fraction (phi(s)), the segregation morphology of PTT/aPET blends is characterized to be the interlamellar segregation morphology when the weight friction of aPET (W-aPET) <= 0.2 and the interlamellar and interfibrillar segregation coexisted when W-aPET > 0.2. The extent of aPET segregation was promoted by increasing aPET composition. POLYM. ENG. SCI., 50:2236-2242, 2010. (C) 2010 Society of Plastics Engineers