<p>In this study, the prepared organically modified montmorillonite/polyvinyl alcohol composite material was applied to polyester fabrics via a padding–baking process to endow them with a certain water-repellent ability. The finished polyester fabrics were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, followed by performance testing including water contact angle, hydrostatic pressure, wash resistance, breaking strength, and air permeability, and the water-repellent effects of polyester fabrics treated with different amounts of organo-montmorillonite were also compared. The results showed that the water contact angle of the finished polyester fabric could reach up to 123.698°, and the hydrostatic pressure was 152.66&#xa0;mmH₂O. After five washing cycles, the water contact angle of the fabric decreased by only about 10%, indicating that the polyester fabric achieved good water-repellent effect, which was attributed to the synergistic effect of organo-montmorillonite and polyvinyl alcohol. Furthermore, the breaking strength of the fabric was significantly improved, with the improvement range ranging from 10% to 35%. This study confirmed that montmorillonite, a natural mineral, can be used as a nanomaterial to construct a nano-rough structure on the fabric surface to achieve water-repellent effect, suggesting that montmorillonite has great potential as a fabric finishing agent.</p>