Binary PEI/PBT blends are prepared using a two-step melt processing method. Miscibility study by MDSC and DMA reveals partial miscibility, and new evidence on the morphological evolution of PEI/PBT blends is presented. Two groups of blends are recognized: PBT-rich blends and PEI-rich blends, as well as phase inversion at concentrations close to 50 wt% of PEI. Mechanical, thermal, and flame resistance performance is influenced by blends morphology, and an opportunity for tailoring blends properties is recognized. Tensile modulus shows synergic contribution for 50/50 and 80/20 blends and yield strength is strongly affected by interfacial adherence between constituents. In addition, elongation at break is compromised by PBT-rich blends morphology, and by PEI-rich blends densification. The 50/50 blend exhibits the best elongational at break result due to its co-continuous morphology. Thermal stability and flammability tests reveal that PEI improves the thermal resistance and charring of PBT, particularly for 50/50 blend.