Composite shells are efficient structural elements that an engineer can use to achieve the highest strength-to-weight and stiffness-to-weight ratios. However, design of composite shells is a very complicated task partly because of the imperfection sensitivity of compressed shells. Buckling of axially compressed composite cylinders has been studied extensively over the years, yet little information can be found in the literature on buckling behavior of these shells under eccentric loading. Buckling of imperfect composite cylinders under concentric and eccentric compression is investigated experimentally and numerically in this paper and particular attention has been given to imperfection sensitivity of the shells. Series of glass fiber reinforced plastic cylinders have been tested under different load eccentricities to validate the corresponding non-linear numerical analyses performed in this study. Good agreement between experimental and numerical results has been achieved through use of ABAQUS/Explicit finite element code and introduction of initial imperfections. Both the experimental and the numerical results show that the knock-down factor increases the increase of the loading eccentricity.