Influences of stiffness distributions on hydroelastic responses of very large floating structures (VLFS) are studied in this paper. Hydroelastic responses are calculated by direct method employing higher-order boundary element method (HOBEM) for fluid analysis and finite element method (FEM) for structure analysis. In structural analysis using FEM, Mindlin plate elements are used. An 1 km-long VLFS with uniform stiffness and modified VLFS with varying stiffness distributions are considered in numerical analysis. Responses of VLFS increase in flexible parts and decrease in stiff Parts. Reduction degree of displacements of VLFS with stiffened center is larger than that of VLFS with stiffened sides.