We show experimental results obtained by an innovative non-destructive approach for the characterization of the damage of composite materials. The analysis regard an aeronautical rotor made of glass fiber–reinforced composite material, and is developed by applying an ultrasonic immersion C-Scan technique. The experimental data are employed in a damage model developed in the context of the Continuum Damage Mechanics theory. In this model, the evaluation of the damage level depends on a synthetic scalar damage parameter, connected to the quantities directly measured in an ultrasonic test, and related to the specific variation of the acoustical impedance. In particular, from the measurement of the ultrasonic velocity in the undamaged and damaged composite, respectively, we evaluated the damage parameter for an artificially damaged GFRP component.