This study investigates the structural performance of concrete-filled steel tubular (CFST) beams through experimental and numerical approaches. The CFST beams are prepared with sawdust as a partial replacement for fine aggregates in concrete. A total of fourteen CFST beams are experimentally tested under four-point bending. The sawdust replacement percentages range from 0 % to 25 %. Mechanical properties of the steel tubes and concrete, including compressive and tensile strengths, are evaluated, and the failure modes, ultimate load capacities, initial stiffness, toughness, and ductility indices are analyzed. The results show that sawdust inclusion significantly influences the flexural strength and ductility of the CFST beams, with optimal performance observed at moderate sawdust replacement levels. In addition, finite element analysis is employed to validate the experimental findings. The numerical model closely approximates the load-deflection behavior and failure mechanisms. The study underscores the potential of using sawdust as a sustainable material in structural applications. The study contributes to resource efficiency while maintaining acceptable performance in flexural load scenarios.