Structural health monitoring (SHM) has become a critical tool for ensuring the safety and serviceability of steel bridges. By enabling early detection of abnormalities and structural deterioration, SHM not only supports timely maintenance but also contributes to optimizing long-term management strategies and reducing lifecycle costs. In Vietnam, the application of SHM has recently legalized for grade I, special infrastructure projects and others large-scale construction works. Nevertheless, the deployment of SHM technology is limited, particularly for old bridge structures. This study presents the development of a health monitoring system for steel bridges, with a case study of a nearly 100-year-old Tan Thuan 1 bridge in Ho Chi Minh City, Vietnam. The results demonstrate the complete process of system design, equipment selection, installation, testing, software development, and warning threshold analysis. For Tan Thuan 1 Bridge, the research achieved a low-cost SHM system that has been validated for stability and can be adapted for use in other structural health monitoring applications.