Multiwalled carbon nanotubes (MWCNTs) were exposed to acid solution containing HNO3 and H2SO4 to synthesis of oxidized MWCNTs and used for preparation of piperazine-based polyamide thin film nanocomposite nanofiltration membrane. Both raw and oxidized MWCNTs were applied in the fabrication of the membranes with four different concentrations of 0.001, 0.002, 0.005, and 0.01 wt. % in the piperazine solution. Salt rejection, permeation, and antifouling properties of unfilled, raw and oxidized MWCNTs embedded membranes were investigated. Water flux for 0.005 wt. % oxidized MWCNTs significantly increased due to this fact that membrane hydrophilicity improved as a result of functionalization of MWCNTs. Contact angle measurements confirmed the improvement of hydrophilicity by adding oxidized MWCNTs to the membranes. Surface SEM and AFM images illustrated that the MWCNTs made surface of the membranes smoother and macro-voids enlargement leads to water flux enhancement. The antifouling properties were investigated using bovine serum albumin (BSA)/salt solution. The results showed that the membranes with a smoother surface had a better resistance against the fouling. The salt rejection performance exhibited that by embedding of the raw MWCNTs and oxidized MWCNTs, improvement in rejecting of Na2SO4 salt can be observed. It could conclude that the addition of both raw and oxidized MWCNTs could improve the desalination performance of the piperazine-polyamide NF membranes. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.