This study presents vibration and lateral buckling optimisation of thin-walled laminated composite beams with channel sections. While flanges' width, web's height, and fibre orientation are simultaneously treated as design variables, the objective function involves maximising the fundamental frequency and critical buckling moment. Based on the classical beam theory, the beam element with seven degrees of freedom at each node is developed to solve the problem. Micro Genetic Algorithm (micro-GA) is then employed as an optimisation tool to obtain optimal results. A number of composite channel-section beams with different types of boundary conditions, span-to-height ratios, and lay-up schemes are investigated for the optimum design. The outcomes reveal that geometric parameters severely govern the optimal solution rather than the fibre orientation and it is considerably effective to use micro-GA compared with regular GA in term of optimal solution and convergence rate.