Molecular relaxation behavior in terms of the alpha, beta, and gamma transitions of miscible PS/PPO blends has been studied by means of DMTA and preliminary work has been carried out using DSC. From DSC and DMTA (by tan delta), the observed cr relaxation (T-alpha or T-g) of PS, PPO, and the blends, which are intermediate between the constituents, are in good agreement with earlier reports by others. In addition, the beta transition (T-beta) of PS at 0.03 Hz and 1 Hz is observed at -30 and 20 degrees C, respectively, while the gamma relaxation (T-gamma) is not observed at either frequency. The T-beta of PPO is 30 degrees C at 0.03 Hz and is not observed at 1 Hz, while the T-gamma is -85 degrees 0 at 0.03 Hz and -70 degrees C at 1 Hz. On the other hand, blend composition-independent beta or gamma relaxation observed in the blends may be a consequence of the absence of intra- or intermolecular interaction between the constituents at low temperature. Thus it is suggested that at low temperature, the beta relaxation of PS be influenced solely by the local motion of the phenylene ring, and that the beta or gamma relaxation of PPO be predominated by the local cooperative motions of several monomer units or the rotational motion of the methyl group in PPO.