This paper proposes a structural optimization method for a hexrotor. Structure here means the positions and orientations of the six rotors constituting the hexrotor. In the present optimization method, 6-DOF dynamic manipulability and the maximum translational acceleration are simultaneously considered as structural evaluation indices. The former is introduced as a common evaluation index for motion performance, and the latter with hope for payload flying against the gravity force. A special class of hexrotor structure is first proposed to make the optimization problem tractable, where 6-DOF dynamic manipulability can be provided by the simple product of translational manipulability and rotational one. Then, structual optimization problems are defined and a nonlinear optimization technique is applied. Here, the optimization problems handle two cases: (i) anti-torque of rotors and change of innertia tensor depending on structure are small enough to be neglected, or (ii) they are explicitly considered for structural optimization. Consequently, it is shown that the optimization provides strong symmetry.