This paper presents an experimental study on deformations and force characteristics of flexible plates both in air and water. The focus is on the complicated interaction problem between the fluid and flexible structures. The displacements and forces of free oscillating plates are measured and compared with each others. The effects of several plate coefficients are investigated i.e. plate thickness, aspect ratio, plate area, plate width ratio, bending angle. For the verification of the experimental results, some of them are compared with numerical simulation and show reasonable agreements.