Membrane‐based pervaporation (PV) has attracted much attention in the dehydration of organic solvents. Permeate pressure and feed flow rate are two important parameters, which affect membrane performance in pervaporation. The effects of these two parameters on the performance of a commercial poly (vinyl alcohol) membrane in the dehydration of benzene have been investigated in this work. The experiments have been carried out at a constant temperature of 60oC, and pressure and feed flow rate range from 1 to 20 mmHg and from 200 to 1200 ml/min respectively. The results indicate that variations in vacuum, especially in permeate pressures of less than 10 mmHg, greatly affect flux and selectivity so that water flux and separation factor increase from 0.98 to 2.63 (gr/hm2) and from 160 to 310 respectively by decreasing permeate pressure from 10 to 1 mmHg. Furthermore, increasing flow rate improves membrane performance only at rates of below 1000 ml/min, and no changes are observed at higher feed flow rates.