As the first step for discussing the reliability of composite structures, a fundamental study is performed to obtain the scattering characteristics of glass-fiber reinforced plastics (GFRP) and woven carbon-fiber reinforced plastics (WCFRP) as well as reference metal. The bending stiffness of materials is evaluated by Euler bucking tests. The experiments are conducted for specified rectangular specimens with simply supported edges. A new attachment to realize the simply support boundary conditions for composite materials have been developed in these experiments. The scattering data in the results for GFRP and WCFRP composites were compared with those of a typical metal of aluminum alloy. The experimental data were compared with numerical simulations including the uncertainties of materials.