The structure of blends of crystalline PEO with amorphous poly(dimethylsiloxane) and poly(methylphenylsiloxane) was studied by polarization microscopy, inverse gas chromatography, and DTA. The concentration dependences of the melting temperature and the degree of crystallinity of these blends were determined. The Gibbs mixing energy of polymers and their blends with chloroform were calculated using the static discrete sorption method, and the data obtained were used to determine the Gibbs energy of polymers mixing with each other according to the thermodynamic cycle. It was shown that the compatibility limit derived from the melting temperature depression of a crystalline component in blends with poly(siloxanes) and the negative values of the Gibbs mixing energy of polymers correspond to the region of small contents of poly(siloxanes) (up to 15-20 wt%) which is in keeping with the solubility of the latter in the amorphous part of poly(ethylene oxide).