Abstract In this thesis, the effect of the orientation of trussed honeycomb core design on the stiffness of a composite honeycomb plate is presented. A commercial finite element (FEM) package ¡¥MSC-MARC¡¦ is employed in the stiffness simulation. To illustrate the feasibility and accuracy of the proposed FEM model, the measured and calculated data for two different sizes regular honeycomb plates (with regular hexagonal cell) are compared. Results show that a good agreement between the simulated and the measured static deflections and dynamic characteristics is found. Numerical results indicate that different orientations of trussed honeycomb core design may improve the stiffness/density ratio of a composite honeycomb plate significantly. The effects of other design parameters of composite honeycomb plate, e.g. width and height of plate, thickness of truss, cell wall and faces, and material of truss, on the stiffness/density ratio have also been investigated in this study.