Nanofiltration (NF) is a cross-flow filtration technology that ranges between ultrafiltration (UF) and reverse osmosis (RO). The nominal pore size of the membrane is typically around 1 nanometre. Nanofilter membranes are typically rated by molecular weight cut-off (MWCO). The MWCO is typically less than 1000 atomic mass units (daltons). The transmembrane pressure required is lower (up to 3 MPa) than used for RO, reducing the operating cost significantly.

Nanofiltration is mainly used for the removal of ions or the separation of different fluids. On a larger scale, the membrane filtration technique is called ultrafiltration, which works down to between 10 and 100 nm.