The application of over-molding processes i.e. polymer-polymer composites, is increasingly being used in automotive industry, offering ample flexibility in terms of design and innovation. However, the mechanical properties are greatly influenced by the compatibility of surfaces between polymer-polymer composites. This study mainly focuses on improving the interfacial adhesion between polymer-polymer composites by modifying the surface properties. Plasma can significantly improve the interfacial adhesion by modifying the surface bond via imparting free radicals. Thermoplastic polymer pairs Polyamide (PA66) - Polyamide (PA6), Polyamide (PA66) - Polybutylene-terephthalate (PBT) and Polyamide (PA66) - Thermoplastic elastomer (TPE) were used to investigate the effect of plasma treatment on interfacial surface adhesion. Proof of concept was conducted in two parts: In the first part, half tensile bars were produced and its process parameters were optimized using design of experiments. In the second part, surface was modified by plasma treatment then, another half tensile bar was over-molded. The surface modification of the polymer was evaluated by an ink test and the interfacial surface strength was measured by tensile testing machine. Additionally, residuals on surface were analyzed by electron microscopy and infrared spectroscopy. Future work will focus on automotive industrial application.