Abstract: A collaborative transportation system composed of two mobile manipulators combines a large operational workspace with high maneuverability, making it well suited for transporting large components. Although conventional mobile-robot path-planning algorithms, such as A^*, are well established, they cannot be directly applied to collaborative transportation scenarios involving inter-robot coupling, configuration constraints, and coordinated manipulator motion. To address the collaborative path-planning problem associated with the coupled configuration of two mobile manipulators, this work proposes an improved A^* method that balances safety, planning efficiency, and kinematic feasibility while ensuring coordinated motion of both manipulators. Compared with RMB-A^* and Dynamic Weighted A^*, the proposed method reduces the planned path length by 7.4% and 1.6%, respectively. It also increases the minimum obstacle clearance by 310% and improves the mean obstacle clearance by 49% and 82% relative to the corresponding reference methods. Collaborative transportation and obstacle-avoidance experiments were conducted on a physical mobile-manipulator platform, and the results validate the effectiveness of the proposed method for coordinated path planning involving two mobile manipulators. The proposed method reduces the manual programming effort required for positioning and coordinating the manipulators, thereby improving the efficiency and safety of large-component transportation.