Abstract: The compatibility,multiple transition and relaxation behaviour of PPS/PES blends and their composites reinforced by carbon fiber (CFPPS/PES) have been studied by internal friction analysis method.The experimental results show that;(1)there is interaction on a molecular-scale between PPS and PES in the blends and the blending ratio is the key facfor to determine the degree of such interaction;(2) there is a rather wide continuous distribution of relaxation times for the secondary relaxation of PES in both the blends and the composites,and the half-width of the relaxation time distribution function for the relaxation process changes with the blending ratio and reaches maximum in the case of 80% PES;(3)PPS and PES are thermodynamically metastable,and heat treatment increases the degree of phase separation of PPS from PES and weakens phase interaction;(4) low temperature therms,l history exerts considerable influence on the glass transition of PPS,the peak height and peak temperature of which decrease with a rise in starting temperature.