This study examines the conversion of oil palm empty fruit bunch (OPEFB) fibre into fermentable sugars for bioethanol production using microwave-assisted phosphinic acid (H₃PO₂) pretreatment. Optimal conditions: 8% H₃PO₂ at 180°C for 60 min yielded 32.62 g L^-1 of reducing sugars, with response surface modelling showing strong accuracy (R² > 0.90). Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed structural changes and increased crystallinity (62.22%–74.06%) after pretreatment. Fermentation with Saccharomyces cerevisiae produced up to 62.17 g L^-1 of ethanol in 48 hr. The results highlight microwave-assisted phosphinic acid pretreatment as an effective method for enhancing sugar recovery and bioethanol yield from OPEFB fibre.