Thin-film composite polyamide membranes were fabricated through cosolvent-assisted interfacial polymerization on a polyvinylidene fluoride (PVDF) hollow fiber support. An m-phenylenediamine (MPD) monomer was dissolved in an aqueous solution containing acetone of varying concentrations. Upon contact of this MPD solution with PVDF, the acetone enhanced the PVDF swelling, resulting in a higher MPD sorption. When an organic phase of toluene comprising a trimesoyl chloride (TMC) monomer was contacted with the wet PVDF, the acetone also enhanced the miscibility between water and toluene, facilitating the diffusion of MPD through the organic phase toward TMC. Hence, MPD cross-linked with TMC at a higher degree. Field emission scanning electron microscopy revealed that the formed polyamide layer grew thicker with increasing acetone concentration. The composite membrane fabricated from using 75 wt% aqueous acetone solution delivered optimal pervaporative dehydration of a 90 wt% aqueous tert-butanol solution: permeation flux = 437.2 g/m(2) h; water concentration = 99.88 wt%. At varying feed temperatures and concentrations, flux increased with temperature but decreased with increasing tert-butanol content. The membrane performance on aqueous n-butanol and isobutanol feed systems was high - 93.47 and 93.37 wt% water in permeate, respectively. Overall, the composite membrane performed well on different aqueous butanol feed solutions.