Several repurpose methods are under development in many ongoing research projects that involve decommissioned wind turbine blades (dWTB) for civil engineering applications, including bridges. The latter field of the dWTB repurposing has been recently the subject of the comprehensive research program carried out by the authors at the Rzeszow University of Technology (RUT), Poland. In order to check the feasibility of using dWTB in bridges, it was necessary to carry out extensive material tests to identify the basic material parameters and the stacking sequence of individual dWTB composites. No this data is usually available after 20–25 years of blades’ usage in wind turbines. However, this data was necessary in repurposing concepts (designs) to check the load-bearing capacity and serviceability of the “new” structures made of the WTB. In a research project carried out by RUT two types of dWTBs were considered for their use in the construction of bridge spans: LM 29.1 from LM Wind Power and V66 from Vestas Wind Systems. A total of several dozen material samples were taken, both from outer shells and spar caps of blades. The stacking sequences and fibre volume fractions were determined by the resin burnout tests. The following mechanical parameters were determined according to ASTM standards: tensile strength and modulus, compressive strength, shear strength, limit strain and Poisson's ratio. Key details of the testing methods and the obtained results for spar cap laminates are provided in the paper. The results of the material testing revealed that the FRP material is still in excellent condition and that the blade has the adequate strength and stiffness to serve as a girder for the bridges.