The study on ``dynamic stiffening'' is currently a focusin the field of flexible multibody system dynamics. A lot of valuableresearches have been done to account for ``dynamic stiffening'' viamathematical model and numerical simulation. However, to one'ssurprise, never had experimental investigations on this problem beenreported. This paper presents experimental investigation on ``dynamicstiffening'' phenomenon. The experiment is based on the prototype of arotating cantilever beam that is often used to discuss the effects of``dynamic stiffening''. The experimental investigation is conducted on asingle-axis air-bearing testbed. A theory model incorporating theeffects of both viscous damping and air drag force is also developedfor the purpose of comparison with experimental results. The phenomenonof ``dynamic stiffening'' is verified by the results of experiment. Thevalidation of the proposed model is confirmed by the experiment, too.