In this work, the nonlinear structural modification/coupling technique proposed recently by the authors is applied to a test system in order to study the applicability of the method to real structures. The technique is based on calculating the frequency response functions of a modified system from those of the original system and the dynamic stiffness matrix of the nonlinear modifying part. The modification can also be in the form of coupling a nonlinear system to the original system. The test system used in this study is composed of two cantilever beams with their free ends held between two thin identical beams which yield cubic stiffness. Thus two linear structures are coupled with a nonlinear connecting element. The frequency response functions of the coupled nonlinear system are measured at several different harmonic forcing levels, and the experimental values are compared with the theoretical values calculated using the nonlinear structural coupling method.