Based on von Kármán-Donnell kinematic assumptions for laminated shells, the nonlinear vibration and postbuckling behaviour of unsymmetrically laminated cross-ply circular cylindrical shells with clamped and simply-supported ends are studied by a multi-mode approach. A solution is formulated which satisfies the associated compatibility equation and all boundary conditions. The transverse equation of motion is fulfilled by the Galerkin procedure. In the case of nonlinear vibration problems, the solution is obtained by the method of harmonic balance. The effect of initial imperfection is also included. Results in nonlinear vibration and postbuckling are presented for different amplitudes of initial imperfection and four sets of boundary conditions. Present results are compared with available data.