Abstract: A dual-arm robot can be appropriately viewed as a mechanical transformer with joint velocity and force as input and cartesian velocity and exerted force of the object as output. This paper presents the direction-oriented manipulability of dual-arm robots, and the velocity and force transmission characteristics under a given posture. The direction-oriented linear/rotation velocity and force/moment manipulability measures are defined. The applications of these indices as optimal performance criterion are explored, and illustrating examples are given out.