Efficient path planning is essential for unmanned surface vehicle (USV) navigation. The A* algorithm is an effective algorithm for identifying a safe path with optimal distance cost. In this study, a modified version of the A* algorithm is applied for planning the path of a USV in a static and dynamic obstacle environment. The current study adopts the A* approach while maintaining a safe distance between the USV and obstacles. Two important parameters-path length and computational time-are considered at various start times. The results demonstrate that the modified approach is effective for obstacle avoidance by a USV that is compliant with the International Regulations for Preventing Collision at Sea (COLREGs).This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.