Bone Tissue Engineering (BTE) and the use of Bone Replacement Materials (BRM) has become a growing field of research during the last decades due to the emergence of regenerative medicine. However, ideal BRM is still not available for the needs of clinical practice due to several limitations of material properties. Biodegradable polyester poly(lactideco-glycolide)/calcium phosphate (PLGA/CaP) is very popular among BRM and often used for BTE applications. Fast material shrinkage of PLGA scaffolds in vivo with loss of its function as a guiding structure for in growing blood vessels and as an osteoconductive construct has been described in the past. In order to receive new information about the in vivo degradation process of these PLGA/CaP scaffolds, Raman Spectroscopy was included in this study to provide further scaffold material analysis at different points of time: PLGA/CaP scaffolds (seeded with or without mesenchmyal stem cells, MSCs) were implanted in a 12.0 mm Critical-Sized Defect (CSD) of the rabbit femur. Animals were sacrificed after 4 and 26 weeks. Samples were then investigated using Micro-computer tomography (μ-CT) and histology. Samples of two animals previously examined were then investigated using Raman Spectroscopy. In fact, the use of Raman Spectroscopy generated new knowledge about the different steps of degradation and material behavior of PLGA/CaP scaffolds in vivo: CaP embedded in and coated on the scaffold was dissolved completely after 4 weeks, and maintenance of the scaffold´s structure and interconnectivity was provided by PLGA alone. Therefore Raman Spectroscopy must be considered as a valuable tool for characterization of BRM and bone tissue in the field of BTE in the future.