Blends of poly(ether ether ketone) (PEEK) and poly(aryl ether sulphone) (PES) have been prepared in the whole composition range. The molecular dynamics and alpha-relaxation behaviour of these materials have been studied using dynamic mechanical and dielectric relaxation spectroscopy. From dynamic mechanical relaxation studies, two alpha-relaxation peaks corresponding to the segmental relaxation process of pure components in the blend was observed. Also, it was found that the temperature at which alpha-process of the homopolymers occurs, shows a slight change with blend composition, corresponding to a PEEK-rich and PES-rich phase. The relaxation intensities of the homopolymers in the blend compared to that in pure state were approximately proportional to their respective content in the blend. From the phase composition of the respective phases obtained using Fox equation, it has been inferred that PEEK dissolves more in PES than vice-versa. The alpha-relaxation of PES could not be detected from dielectric relaxation spectroscopy because of the possible influence of do conduction and electrode polarization losses. Otherwise, the alpha-relaxation behaviour of PEEK-rich phase observed from dielectric relaxation studies agree with those inferred from dynamic mechanical relaxation studies. Furthermore, activation energies for molecular motions (E-a) at the alpha-relaxation have also been determined using an Arrhenius form of equation and it has been found that E-a for both PEEK-rich and PES-rich phase show variation with composition. Similarly, the relaxation times associated with the mobility of relaxing species in both PEEK and PES are influenced in the blends. It is likely that these observations are related to some interactions and a partial segmental mixing between the blend components, which result in changes in the local molecular environment on blending.