Hexrotor UAVs have six rotor propellers and can control their own position and orientation, individually. This paper proposes a method to optimize the hexrotor structure. The optimization is evaluated by dynamic manipulability and the maximum translational acceleration. The class of structure optimized in this paper is defined so that dynamic manipulability in six-dimensional space can be expressed by the product between
translational 3-dimentional space and rotational space. Here, this class includes wide varieties of hexrotors. The resulting structure is given by the optimization via a nonlinear programming algorithm. Also, The relation between the number of optima and their structures are studied.