Polysulfone (PSU)/poly(ethylene terephthalate) (PET) blends were obtained by direct injection molding across the composition range. Their phase behavior, thermal properties, morphology, and mechanic at properties were measured. The blends were composed of a pure PSU amorphous phase and either a pure PET phase in PSU-poor blends, or a PET-rich phase with some dissolved PSU in PSU-rich blends. The morphology of the dispersed phase was mostly spherical with some elongated particles in the PET-rich blends. A slight synergistic behavior was observed in the Young's modulus, mainly in the 90/10 blend, which is probably due to orientation effects. The presence of some broken particles indicated some interfacial adhesion. The ductility values were approximately linear with composition. This was generally the case in PSU-rich blends, and was attributed to the higher level of PSU in the PET-rich phase. Although embrittlement was seen in blends with 30% of the second component, the ductility of the two pure components did not significantly decrease after annealing due to the presence of low amounts (up to 10%) of another component of the blend. (C) 2004 Wiley Periodicals, Inc.