In this study, a few nanofiltration membranes were prepared by dissolving the blend of polyethersulfone/polyimide in dimethylformamide (DMF). Then, the prepared membranes were modified using new synthesized modifiers. We used methanol solution comprising 10 wt.% ethylenediamine (EDA) as a cross-linker to open imide group rings. PEG-triazine as a new modifier material, which was produced in the laboratory, was used in different concentrations (0.3 and 0.7 wt.%). Finally, trimethylamine (TMA) was added to complete the modification. This modification involves the formation of a covalence –C–N– bond between PEG-triazine and amine groups (according to addition-elimination reactions) at different temperatures. SEM, AFM, FTIR-ATR and contact angle measurements were used for membrane characterization. Rejection capability and flux of the obtained membranes were investigated by NaCl solution as feed using nanofiltration set-up. The hydrophilicity of PES/PI membranes was changed by modification. By adding the EDA and PEG-triazine, a decrease in NaCl flux (to 75 kg/m2 h) and an increase in NaCl rejection (to 20%) were observed. By introducing TMA into the membrane recipe, the membrane flux increased from 75 until about 100 kg/m2 h. The flux measurement of PEG 600 solution demonstrates that TMA-modified membrane has lower flux decline during the filtration process.