The postbuckling behavior of graphite-epoxy laminated stiffened panels has been studied analytically and experimentally herein. In this research, the stiffened panels were analyzed using the nonlinear finite element method. The progressive failure analysis adopted the maximum stress criterion and the complete unloading failure model. In the failure analysis, the considered failure modes were matrix failure, shear failure and fiber failure. The stiffeners were formed by the continuous lay-up of the skin to improve the integrity of the stiffened composite panels. A shadow moire technique was used to monitor the out-of-plane deformation of the skin panel. Piezoelectric film sensors were used to detect the failure events during experiments. The analytical results on the buckling load, postbuckling behavior, and postbuckling compressive strength showed good agreement with the experimental results. Parametric studies were conducted to show the effects of stacking sequences and stiffener shapes on the buckling load and postbuckling compressive strength of stiffened composite panels.