The deformation behavior and stress-strain relationships for a lightweight sandwich plate in the elastic regions are mainly dependent on the elastic properties of the core in the sandwich plate. The aim of this paper is to determine experimentally the elastic properties of a core in a thin sandwich plate with a metallic truss core. Three-points bending experiments were performed to obtain a linear relationship between compliance per span length and the square of the span length for the designed sandwich plate. The specimen was manufactured from the continuous multi-points resistance welding of SUS 3O4H sheets and crimped metallic truss cores. The elastic and shear moduli of the core were estimated by the slopes and the intercepts of the linear relationship, respectively. Through the comparison of the shear moduli and force-deflection considering the core stiffness with those disregarding the core stiffness, it was shown that the core stiffness should be considered to estimate accurately the elastic and shear moduli of a core as well as the force-deflection curves of a thin sandwich plate with a metallic truss core. The contribution ratios of the bending and shear deflections of the thin sandwich plate to the total deflection were investigated. In addition, the influence of the crimping angle on the elastic properties, the force-deflection curves, and the contribution ratios of both bending and shear deflections to the total deflection was examined.