The main motivation for this study is to verify the applicability of OpenFOAM to Fluid-Structure Interaction (FSI) problem for the use of nuclear power plant flow simulation. In order to verify the applicability to the problem, the pendulum in fluid simulation, which represent a classical FSI problem, has been performed with deformable mesh, which is commonly used FVM-based method. Fluent with a User-Defined Function (UDF) as well as OpenFOAM is used for comparison. The results of the present study shows the good agreement of amplitude damping between OpenFOAM and Fluent. Based on this research, further study using OpenFOAM is proposed.