AbstractTailoring the well-defined nanochannels of ultrafiltration membranes from self-assembled block copolymers (BCPs) toward the nanofiltration regime can expand their potential applications in the fractionation or separation of small molecules. One big issue is to fabricate a nanofiltration membrane with high permeance, good selectivity and excellent fouling resistance. Here such a membrane is presented using a tailor-made diblock copolymer composed of a hydrophobic major block and an amphiphilic minor block. A scalable integral asymmetric isoporous membrane is fabricated by the solvent evaporation induced co-assembly of BCP and in situ formed inorganic titanium dioxide nanoparticles combined with nonsolvent induced phase separation. The membrane nanopores are readily post-functionalized using negatively charged moieties by straightforward in situ gas–solid reactions. The potential to use the post-functionalized membrane for separation of small organic molecules having 1–2 nm lateral dimensions (having molecular weights in the range of 300–1500 g mol−1) is demonstrated. The negatively charged membrane displays high flux, excellent antifouling properties with a low permeation flux decline and nearly complete flux recovery. This type of membrane is a promising candidate for a new generation of nanofiltration membranes.