The miscibility of PVC blends (PVC/PMMA and PVC/PEO) was investigated. Experiments using viscosimetry and differential scanning calorimetry (DSC) were performed. The presence of attractive forces among polymers was evaluated according to the Sun theory by the determination of the alpha parameter from the viscosimetric data. The melting depression in a binary blend is an indication of miscibility. Viscosimetric and thermal analysis showed that the PVC/PMMA and PVC/PEO blends are miscible. The miscibility of the PVC/PMMA and PVC/PEO blends is explained in terms of donor-acceptor interactions between chlorine atoms (a weak acceptor species) of PVC and oxygen atoms (a donor species) of the PMMA and PEO.