This book constitutes the refereed post-conference proceedings of 4th International Symposium on Intelligent Unmanned Systems and Artificial Intelligence, SIUSAI 2025, in Hohhot, China, during August 15–17, 2025. The 37 full papers presented in this volume were carefully reviewed and selected from 99 submissions. The papers are organized in the following topical sections: Perception and Scene Understanding for Intelligent Unmanned System; AI-Driven Control, Planning and Decision-Making; Predictive Modeling and Data Intelligence for Autonomous Operations.