Purpose This study aims to reduce the interfacial tension by increasing the better adhesion between different immiscible polymers phases and also to evaluate the mechanical, thermal and thermo-mechanical behavior of the immiscible polymer blends. Design/methodology/approach The polymer blend composite (PBC) was prepared using a twin-screw extruder followed by injection molding. Two different kinds of PBC with compatibilizer (Ethylene-n-Butylacrylate-Glycidyl methacrylate) of varying compositions like polybutylene terephthalate + poly trimethylene terephthalate and polybutylene terephthalate (30% glass filled) + poly trimethylene terephthalate were prepared and material behavior at various test conditions were studied. The effect of glass fiber reinforcement on polymer blend and the interlocking effect by the compatibilizer between the polymer phases were also assessed. Findings Mechanical behavior of PBC was estimated by tensile, flexural and angular impact tests. Likewise, the thermal deflection was studied with the help of heat deflection temperature test. Thermo-mechanical behavior likes storage modulus, loss modulus and loss tangent were studied using the dynamic mechanical analysis test. Morphological analysis was characterized using field emission scanning electron microscopy. Originality/value This in turn makes the process easy to obtain the PBC having inherent mechanical, thermal and thermo-mechanically stable. And, it also enhances the mechanical properties like tensile, flexural and impact strength. Simultaneously, posse’s excellent heat deflection and thermo-mechanical behavior over a temperature range of 35–140ºC at a constant frequency of 5 Hz.