Physical aging in poly(ethylene oxide)(PEO)/atactic-poly(methyl methacrylate) (a-PMMA) blends with a low content of PEO is discussed. Behaviour in the T-g-region is analysed. Different compositions are prepared by mixing in the melt, and were compared at the same temperature distance to mid-point enthalpic T-g. Macrolevel properties (enthalpy and external volume) are discussed in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. In particular, the non-linearity x parameter (determined using the peak shift method), the apparent activation enthalpy Delta h*, and the combination theta.(I-x), where theta = Delta h*/R.T-g(2), are used to discuss overall segmental co-operativity and relaxation in the blends. Based on aging in viscoelastic properties (aging rate), structural mobility is discussed. From obtained results, an increase of co-operativity, and decrease of both, relaxation rate and change of structural mobility, with the increasing content of PEO in the blend, is concluded for temperatures between the dilatometric and enthalpic T-g. Agreement with data from studies at the microlevel by other authors, where an onsetting with time phase separation in PEO/PMMA has been postulated, is found.