The presence of cracks or similar imperfections can considerably reduce the buckling load of a shell structure. In this paper, buckling analysis of cylindrical shells with a longitudinal crack is presented. Numerical buckling analyses of cylindrical shells were performed using FEM, and verified by experiment. The numerical analyses and experiments were conducted for several crack lengths and radius of curvature, and two different boundary conditions were applied, i.e. simply support and clamp in all sides. The results show the effect of the presence of crack to the critical buckling load of the shells. There are good agreements between experimental and numerical results.