The mobile platform-manipulator welding system discussed in this paper is a three-link manipulator mounted on a mobile platform. This system uses laser range sensors to guide the mobile platform and a vision sensor to guide the manipulator end-effector to the weld seam line accurately. The task is to track the horizontal fillet seam in the grillage assembling method, which is one of the conventional procedures for assembling the flat hull blocks in shipbuilding and consists of only the horizontal fillet seam. In this paper, the path planning for the combined motion of the mobile platform and the manipulator was presented concerning manipulability measure and characteristics of the welding process. A control method for the mobile manipulator was presented, and simulation results were also presented to demonstrate the effectiveness of the control method for horizontal fillet welding. (C) 2001 Published by Elsevier Science Ltd.