Through the recent researches on hydroelastic responses of Very Large Floating Structures (VLFSs), it has been found that the wave-induced elastic responses of a simple mat-like VLFS of homogeneous rigidity are quite larger than anticipated. Because of this fact, if a VLFS is to be used such purposes as a floating airport, certain measures should be employed in order to attenuate the elastic responses. The objective of the present study is to optimize the geometry, rigidity and other things of a VLFS in such a way that the elastic responses are minimized. As a first report, a comprehensive parametric study is conducted on the wave-induced elastic responses of VLFSs while varying their geometries, rigidity and supporting columns as the parameters and the possibilities of the reduction of elastic responses are investigated.