Axial flux brushless DC (BLDC) motors are being developed for many applications due to their attractive features, and they can be designed to have a higher power-to-weight ratio resulting in less core material. In this paper double sided structure of axial flux BLDC motors are designed and optimized separately using by particle swarm optimization (PSO) algorithm. Optimized structures are compared due to their output power density, and the best structure is selected. Finally, the sensitivity analysis of design parameters such as pole arc ratio, diameter ratio, airgap and airgap flux density is performed for selected structure.