A wake-oscillator model is proposed for predicting vortex-induced vibration (VIV) in a 4:1 rectangular cross-section cylinder. The model incorporates two oscillators: one on the rear face simulating wake vortex swaying, and another on the windward face representing main vortex variations. Governing functions are derived based on the zero circulation assumption, and parameters are determined through rigid and aeroelastic model tests. The model's validity is confirmed by comparing predicted response amplitudes with experimental data, showing effective prediction across various Scruton numbers. The model is further used to investigate VIV excitation mechanisms, focusing on wind load and vibrating frequencies of the oscillators. This helps understand structural VIV phenomena. VIV is a typical large amplitude vibration in slender structures with low damping, such as high-rise buildings, long-span bridges, transmission cables, and marine risers. Understanding VIV is vital for wind-resistance design. Research has shown that structural damping significantly affects VIV response. Numerical and experimental methods are time-consuming, so mathematical models are developed for efficient prediction. Two popular models are the self-excitation force model and the wake-oscillator model. The self-excitation force model describes VIV as resulting from a self-excitation force, but it lacks physical explanation. The wake-oscillator model, based on dynamic system perspectives, has been used to predict VIV responses. However, existing models are not suitable for cylinders with large aspect ratios due to unique flow fields. The 4:1 rectangular cross-section cylinder is a fundamental model for wind-induced vibration analysis. This study proposes a novel wake-oscillator model tailored for 4:1 rectangular cylinders, based on the Tamura model. The model is derived to capture VIV characteristics, including structural vibration amplitude and lock-in phenomenon, and is validated through experimental data. This model provides a more accurate prediction of VIV in cylinders with larger aspect ratios.A wake-oscillator model is proposed for predicting vortex-induced vibration (VIV) in a 4:1 rectangular cross-section cylinder. The model incorporates two oscillators: one on the rear face simulating wake vortex swaying, and another on the windward face representing main vortex variations. Governing functions are derived based on the zero circulation assumption, and parameters are determined through rigid and aeroelastic model tests. The model's validity is confirmed by comparing predicted response amplitudes with experimental data, showing effective prediction across various Scruton numbers. The model is further used to investigate VIV excitation mechanisms, focusing on wind load and vibrating frequencies of the oscillators. This helps understand structural VIV phenomena. VIV is a typical large amplitude vibration in slender structures with low damping, such as high-rise buildings, long-span bridges, transmission cables, and marine risers. Understanding VIV is vital for wind-resistance design. Research has shown that structural damping significantly affects VIV response. Numerical and experimental methods are time-consuming, so mathematical models are developed for efficient prediction. Two popular models are the self-excitation force model and the wake-oscillator model. The self-excitation force model describes VIV as resulting from a self-excitation force, but it lacks physical explanation. The wake-oscillator model, based on dynamic system perspectives, has been used to predict VIV responses. However, existing models are not suitable for cylinders with large aspect ratios due to unique flow fields. The 4:1 rectangular cross-section cylinder is a fundamental model for wind-induced vibration analysis. This study proposes a novel wake-oscillator model tailored for 4:1 rectangular cylinders, based on the Tamura model. The model is derived to capture VIV characteristics, including structural vibration amplitude and lock-in phenomenon, and is validated through experimental data. This model provides a more accurate prediction of VIV in cylinders with larger aspect ratios.