This paper introduces a novel wake-oscillator model designed to predict vortex-induced vibration (VIV) in a 4:1 rectangular cylinder. VIV is a significant issue in the wind-resistance design of slender structures, and predicting its amplitude and wind speed range is crucial. The proposed model employs two oscillators: one on the rear face to simulate the swaying motion of the wake vortex and another on the windward face to represent variations in the main vortices generated from the leading edges. The governing functions of these oscillators are derived based on the zero circulation assumption, and their parameters are determined through rigid and aero-elastic model tests. The model's effectiveness is validated by comparing predicted response amplitudes with experimental data, demonstrating its ability to accurately predict VIV across various Scruton numbers using a single set of parameters. The study also investigates the underlying mechanics of VIV excitation, focusing on the wind load and vibrating frequencies of the oscillators, providing insights into the structural VIV phenomenon.This paper introduces a novel wake-oscillator model designed to predict vortex-induced vibration (VIV) in a 4:1 rectangular cylinder. VIV is a significant issue in the wind-resistance design of slender structures, and predicting its amplitude and wind speed range is crucial. The proposed model employs two oscillators: one on the rear face to simulate the swaying motion of the wake vortex and another on the windward face to represent variations in the main vortices generated from the leading edges. The governing functions of these oscillators are derived based on the zero circulation assumption, and their parameters are determined through rigid and aero-elastic model tests. The model's effectiveness is validated by comparing predicted response amplitudes with experimental data, demonstrating its ability to accurately predict VIV across various Scruton numbers using a single set of parameters. The study also investigates the underlying mechanics of VIV excitation, focusing on the wind load and vibrating frequencies of the oscillators, providing insights into the structural VIV phenomenon.