An unbalanced and asymmetric sandwich composite structure consisting of Titanium 6-4 and glass-reinforced plastic (GRP) skins with a phenolic honeycomb core is being considered for construction of a surface ship mast which will enclose critical shipboard equipment. Stability of the structure is one of the major concerns in the design process. This research focuses on analytical and experimental studies of an unbalanced composite sandwich beam subjected to a compressive axial load. The failure load (i.e., peak load) and failure mode of each skin material and the sandwich construction were measured at the laboratory. An analytical model was developed for predicting the failure load of the unbalanced and asymmetric sandwich composite configuration, including the transverse shear energy of the core material. The experimental data agreed very well with analytical prediction. Postbuckling failure, as well as residual strength after initial failure, were also studied.