An effective joining between polypropylene (PP) and polybutylene terephthalate (PBT) is closely related to bonding between PP and PBT. The objective of this study is to improve the bonding between PBT and PP with a compatibilizer application between joints as tie-layer at various concentrations. Flexural strength, lap-shear strength and interlaminar shear strength of joined parts were determined to determine the adhesive bonding performance. The fracture behavior of the bonds was also investigated. It was found that using compatibilizers in a PP/PBT joining system improved the mechanical characteristics. Improved results were obtained with increasing ratios of compatibilizers in tie-layer and maximum mechanical results were achieved for 100 % compatibilizer usage in PP-PBT system.