In this paper, the effects of initial imperfections on the buckling behavior of thick cylindrical shells and curved panels are investigated. It is assumed that the shell has an axisymmetric and periodic initial imperfection in the axial direction. The shell is assumed to have different boundary conditions and subjected to pure external pressure loading. Governing differential equations are developed on the basis of the second Piola-Kirchhoff stress tensor and are reduced to a homogenous linear system of equations using the differential quadrature method. The effects of different boundary conditions, geometric ratios; curvature and imperfection parameter on the buckling behavior of isotropic thick cylindrical shells and curved panels are carefully discussed. The results obtained by the present method are verified with finite element solutions and those reported in the literature.