The miscibility and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends have been investigated by differential scanning calorimetry (DSC) and optical microscopy. PET/PEI blends were prepared by solution precipitation from two solvents : a phenol/tetrachloroethane mixed solvent and dichloroacetic acid. It was found that the compatibility of the as prepared blends depended on the solvent used. Dichloroacetic acid appeared to provide better segmental mixing for PET and PEI than the mixed solvent of phenol and tetrachloroethane. The compatibility of the blends as prepared from both solvents could be enhanced by melt annealing. The composition dependence of T-g of PET/PEI blends exhibited a cusp at the composition of w(PEI) approximate to 0.60 and was analyzed using the classical Gordon-Taylor’s equation and the free volume theory of Braun-Kovacs. The PET crystallinity measured from the enthalpy of melting displayed a monotonic drop with increasing PEI content in the composition range of w(PEI) > 0.4, while it stayed approximately constant for w(PEI) < 0.4. The effect of blending with PEI on the multiple melting behavior of PET was also investigated. The highest melting endotherm was found to diminish with increasing PEI content in the blends, showing that the recrystallization of PET after the initial melting was hindered by the presence of PEI. After the crystallization of PET, a strong segregation of PEI was observed. Such segregation of PEI was accompanied with a significant increase in spherulitic nucleation density. The monitoring of the T-g shift during crystallization and the morphological observation by optical microscopy suggested that the crystallization was coupled with a liquid-liquid phase separation, where the miscible melt demixed into the PET-enriched phase and the PEI-rich phase. The morphology created by the liquid-liquid phase separation and the nucleation at the domain interfaces may account for the drastic increase in nucleation density.