A super-ductile PBT alloy with excellent heat resistance was successfully fabricated by reactive blending of poly(butylene terephthalate) (PBT) with poly(ethylene-co-glycidyl methacrylate) together with linear low density polyethylene (LLDPE) and hydrogenated styrene-butadiene-styrene block copolymer (SEBS). It possesses a unique tensile stress-strain curve with no yielding point and large elongation at break, moreover, the alloy did not show serious deterioration of the mechanical properties by high temperature annealing at 150 degrees C for 96 h. The structure-properties relationship is discussed on the basis of transmission electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, and wide-angle X-ray diffraction analysis. The outstanding ductile nature seems to come from the negative pressure effect of LLDPE (or LLDPE/SEBS) particles that dilates the PBT ligament matrix to enhance the local segment motions.