Organic solvent nanofiltration (OSN) is an emerging membrane separation technique with a great potential for various industrial branches. The most popular polymers used as membrane material for OSN, are the polyimides (Pis). Pls polymers have excellent thermal, oxidative and mechanical stability. Moreover, the crosslinking by thermal treatment, UV irradiation or chemical reaction, confers to the PI membranes high chemical resistance to various organic solvents. Asymmetric PI membranes are usually prepared by non solvent induced phase separation (NIPS). Thin-film composites (TFC) membranes have been also realized in which a thin selective layer of polydimethylsiloxane (PDMS) is cast on PI support layer. In addition, TFC membrane have been prepared by interfacial polymerization of polyamide (PA) on a PI support. These composite membranes have the advantage over the asymmetric ones that each layer can be optimized independently.