In this study, poly(vinyl alcohol) (PVA) hybrid membranes with zeolitic imidazolate framework-90 (ZIF-90) particles were fabricated by the viscosity-driven in situ self-assembly of ZIF-90 particles in a PVA matrix and were employed for ethanol dehydration via pervaporation (PV) technology. By this method, the size-controlled and well-distributed ZIF-90 particles were successfully embedded into PVA membranes. Based on the cross-linking reactions between the ZIF-90 particles and the PVA matrix, the ZIF-90/PVA hybrid membranes demonstrated higher mechanical strength, swelling resistance, and a high separation performance for ethanol dehydration. The ZIF-90/PVA hybrid membranes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, a mechanical test, and water contact angle measurements. The effects of the ZIF-90 particle size, loading level, thermal treatment temperature, operation temperature, and the feed compositions of the PVA hybrid membranes on the PV performance were systematically explored. Accordingly, the hybrid membranes exhibited excellent water permeability and selectivity for water–ethanol mixture separation. Specifically, the ZIF-90/PVA hybrid membrane (M-8), which was treated thermally at 130 °C, exhibited its optimal PV performance at a flux of 268 g/(m² h) and a separation factor of 1379 for the PV dehydration of the 90 wt% ethanol aqueous solution at 30 °C. The ZIF-90/PVA hybrid membranes exhibited excellent potential in the PV application for ethanol dehydration.