This paper describes a parallel genetic algorithm for optimal synthesis of the internal mechanism for a morphing aerofoil. Treating the number of precision points as a design parameter leads to an optimisation problem with a variable number of design parameters and hence variable-length chromosomes in its corresponding genetic algorithm. The objective of the optimisation is to minimise the weight of the mechanism subject to a constraint on the permissible deviation of the morphed aerofoil from its target shape. Decomposition of the optimisation algorithm into two parallel algorithms is realised by dividing the original problem into two problems. In the first optimisation process, using an approximated objective function, sub-optimised solutions are produced. These solutions then are passed into the second optimisation process with the original objective function. The proposed genetic algorithm has been compared with a conventional genetic algorithm with respect to its computational efficiency, showing a significant improvement in computational time.