Optimum design of laminated composite sandwich plates with both continuous "core thickness# and discrete "layer group _ber angles and thicknesses# design variables subjected to strength constraint is studied via a two!level optimization technique[ The strength of a sandwich plate is determined in a failure analysis using the TsaiรWu failure criterion and the _nite element method which is formulated on the basis of the layerwise linear displacement theory[ In the _rst level optimization of the design process\ the discrete design variables are temporarily treated as continuous variables and the corresponding minimum weight of the sandwich plate is evaluated subject to the strength constraint using a constrained multi!start global opti! mization method[ In the second level optimization\ the optimal solution obtained in the _rst level opti! mization is used in the branch and bound method for solving a discrete optimization problem to determine the optimal design parameters and the _nal weight of the plate[ Failure test of laminated composite foam! _lled sandwich plates with di}erent lamination arrangements are performed to validate the proposed optimal design method[ A number of examples of the design of laminated composite foam!_lled sandwich plates are given to demonstrate the feasibility and applications of the proposed method[ ร 0888 Elsevier Science Ltd[ All rights reserved[ Keywords] Composite materials^Sandwich plates^Laminates^Optimization^Finite element method^First!ply failure^Stress analysis