Employing segmental interaction densities (B-ij’s) determined by means of analogue calorimetry, a binary interaction model based on the Flory-Huggins theory predicts the miscibility of poly(ethylene oxide) (PEG) with poly(methyl methacrylate-co-ethyl methacrylate) [P(MMA-co-EMA)] copolymers having high methyl methacrylate contents. The miscibility behavior of PEO with P(MMA-co-EMA) containing 60 wt % methyl methacrylate was investigated in blends prepared by four different mixing methods. The miscibility in the amorphous state was studied by differential scanning calorimetry (DSC), dynamic-mechanical thermal analysis (DMTA), and solid-state C-13 NMR spectroscopy techniques. Glass transition (T-g) and alpha-relaxation (T-a) results shown miscibility for blends with PEO content lower than 20 wt %. Blends with PEO content higher than 20-40 wt % show both T-g and T-a values very similar to those of pure PEG. The presence of a second amorphous phase composed of PEO and the copolymer could only be detected by DMTA. The intimacy of mixing in this amorphous phase was supported by C-13 NMR. The melting and crystallization behavior was also investigated. The small depression in the experimental melting temperatures did not allow a definite conclusion about the homogenity of this system in the molten state to be obtained. The addition of the copolymer did not have a great influence on the spherulite growth rate of PEG, this behavior being that expected of a multiphasic blend. Moreover, a new analysis proposed in this paper was able to explain the crystallization behavior of these blends, assuming that diffusion takes place from an immiscible melt. These results are in good agreement with the miscibility predictions from model compound mixtures.