Compression tests were performed on debonded sandwich beams made of graphite/epoxy face-sheets and aramid fiber honeycomb core. The sandwich beams were manufactured using a vacuum bagging process. The face-sheet and the sandwich beam were co-cured, thus the excess resin from the graphite/epoxy prepregs was used to bond the face-sheet and the core. Delamination between one of the face sheets and the core was introduced by using a Teflon® layer during the curing process. Axial compression tests were performed to determine the ultimate load carrying capacity of the debonded beams. Double Cantilever Beam tests were performed to determine the fracture toughness of the face-sheet/core interface. It was concluded that linear buckling analysis was inadequate for predicting the ultimate loads. A post-buckling analysis was carried out using a nonlinear plane finite element model of the sandwich beam. The ultimate loads predicted by the finite element model were reasonably good for specimens with long delaminations.