Co-extrusion of polymers is a powerful tool to produce multilayer composites that combine properties which cannot be achieved by pure substances alone. The strength of the total composite is determined by the adhesion between the adjacent layers. The polyolefins used in industrial applications often are non-polar and show low surface free energy which impairs the overall adhesion. Different adhesion mechanisms for polymers were proposed in the literature. One widely accepted model is based on interdiffusion of the materials and the formation of an interface layer. The aim of the study is to characterize the interdiffusion layer of a co-extruded polypropylene-based composite by confocal Raman spectroscopy. With Raman spectroscopy, the chemical composition of the substances in the bulk layers as well as at the interface can be determined. In the characterized seven-layered systems, a polyethylene- and vinyl alcohol-based barrier layer is combined with a maleic acid grafted polypropylene adhesive, pure polypropylene and a regrind material. The different layers can be clearly differentiated, and the presence of interface layers with spectral properties deviating from the pure substances can be observed. In addition, a three-layered polypropylene based system is investigated, whose characterization shows the limitations of the confocal Raman spectroscopy.