Purpose: To determine the mechanical strength and stiffness of the new 2.1 mm biodegradable ultrasound-activated SonicWeld Rx (Gebrüder Martin GmbH & Co, Tuttlingen, Germany) osteofixation system in comparison with the conventional 2.1 mm biodegradable Resorb X (Gebrüder Martin GmbH & Co) osteofixation system. Materials and Methods: Plates and screws were fixed to 2 polymethylmethacrylate blocks to simulate bone segments and were subjected to tensile, side bending, and torsion tests. During testing, force and displacement were recorded and graphically presented in force-displacement diagrams. For the tensile tests, the strength of the osteofixation system was measured. The stiffness was calculated for the tensile, side bending, and torsion tests. Results: The tensile strength and stiffness as well as the side bending stiffness of the SonicWeld Rx system presented up to 11.5 times higher mean values than the conventional Resorb X system. The torsion stiffness of both systems presents similar mean values and standard deviations. Conclusions: The SonicWeld Rx system is an improvement in the search for a mechanically strong and stiff as well as a biodegradable osteofixation system. Future research should be done to find out whether the promising in vitro results can be transferred to the in situ clinical situation.