The miscibility and phase behaviour of poly(hydroxy ether of bisphenol-A) (phenoxy)/poly(methyl methacrylate) (PMMA) blends were investigated using Raman microscopy. It was shown that while phenoxy/PMMA blends prepared by casting from chloroform at room temperature are immiscible, the blends prepared at high temperature are miscible. The Raman technique revealed the shift of the PMMA carbonyl stretching band in the miscible blends and its absence in the immiscible blends. This may be explained by the presence of specific interactions between the groups in phenoxy and PMMA due to the increased chain mobility during the mixing at high temperature. The changes of the special features in the Raman spectra were found to be useful in identifying different phase structures and their compositions in the blends.