In applications where the water hardness and TDS were marginally higher, the nano-filtration membrane came in very handy due to its ability in reducing the permeate TDS at reasonable energy cost. In this work, a thin nanofiltration membrane formed by M-phenylenediamine (MPD) and trimesoyl chloride (TMC) and coated on both sides of a polyacrylonitrile (PAN) membrane. Interfacial polymerization method was used for the nano-film formation. Tests showed that thick monomers solution and denser PAN structure would lead to a membrane of better solutes rejection.