The miscibility behaviour of melt-mixed poly(ethylene terephthalate-co-diethylene glycol terephthalate) [PET-co-DEGT] with poly(ethylene oxide) was investigated in all composition ranges. The crystallization of the semicrystalline blend component at different compositions was evaluated by optical microscopy with crossed polarizers. Thermal analysis (d.s.c., t.g.a. and DMA) indicate that the system is miscible in the composition of some components, and partially miscible in other ranges of composition. For PET-co-DEGT/PEO mixtures there was a reduction in the fusion enthalpy of the semicrystalline component, showing favourable interactions between these polymers, with some influence on the PEO crystallization.