This paper presents a study for the optimal design of the postbuckling behaviour of rectangular laminated composite plates under axial compression. In the optimisation process, lamination parameters are used as the intermediate design variables to characterise composite plates. Using perturbation analysis, an asymptotic closed-form solution is derived to model the postbuckling behaviours of orthotropic laminated composite plates under axial compression. The closed-form solution offers an efficient means to compute the structural response. Furthermore, the relatively high accuracy of the asymptotic model that has been developed facilitates optimal design of composite plates in the postbuckling regime. The postbuckling design criteria of composite laminated plates are based on the minimisation of either the maximum normal displacement or the end-shortening strain for a given compressive load. The optimisation process is split into two-steps. At the first step, a gradient-based mathematical programming is used to determine the optimal lamination parameters. Subsequently, realistic laminate layups are retrieved from the optimal lamination parameters using a genetic algorithm. Optimisation results for the composite plate with different aspect ratios are computed and discussed.