This book gathers the proceedings of the 4th International Conference on Structural Engineering Research (iCSER), held in Sydney, Australia on November 20-26, 2025. Contributions include a wide range of topics in structural engineering such as Building and bridge structures, Composite structures, Large-scale infrastructure and spatial structures, Prefabricated structures, Fire engineering, Earthquake engineering, Performance-based design and analysis, Numerical analysis of structures using finite element modelling, Disaster-prevention and hazard mitigation, Reliability and durability of structures, Construction monitoring and control for large-scale structures, Structural rehabilitation, retrofitting and strengthening, Wind engineering, Theories and methods of structural analysis.