In this paper, we present the initial buckling and post-buckling responses of axial loaded advanced grid stiffened (AGS) composite cylindrical shells with reinforced rectangular or circular cutouts. The AGS cylindrical shells were reinforced by various local grid configurations near the cutout areas. The effects of different reinforcing grid configurations on critical loads were then examined and compared to those of different skin-reinforcing designs using Finite Element Analysis (FEA) simulations. A high-fidelity non-linear analysis procedure was proposed to predict the non-linear buckling response of the shell structures. The simulation results indicated that the grid reinforcements can reduce or eliminate the risk of local buckling response near the cutout areas and increase the critical load of the shell more effectively than the skin reinforcements. Furthermore, those results showed that an optimum grid reinforcement configuration exists, which significantly improved the initial buckling and post-buckling resistance of the cylindrical shells under axial loading. The above findings can potentially be useful to the analysis and optimum design of AGS composite cylindrical shells with cutouts. © 2012 Published by Elsevier Ltd.