The phase behaviour of the binary polymer system consisting of poly(hydroxy ether of bisphenol A) (Phenoxy) and poly(styrene-co-acrylonitrile) (SAN) has been investigated by means of visual observations, light transmission measurements, differential scanning calorimetry and dynamic mechanical thermal analysis. The influence of both the blend composition and the copolymer composition of SAN on the miscibility of these binary blends was examined. All of the Phenoxy/SANx (x=5, 10.4, 15, 16.9, 29, and 34 wt% AN) blends studied were partially miscible. The composition of the two phases and the interaction parameters were calculated from measurements based on the glass transition temperatures.