Thin film composite (TFC) type positively-charged nanofiltration membranes, bearing fixed quaternary ammonium moieties, have been developed and studied. Branched polyethyleneimine (PEI) was functionalized by reaction with glycidyl trimethyl ammonium chloride (GTACl) to introduce quaternary ammonium chloride. Positively-charged TFC membranes were prepared by in situ interfacial polymerization of functionalized PEI and terephthaloyl chloride. The effects of variation of chemical compositions and other experimental conditions such as curing temperature and duration of curing on the performances of the membrane were studied. ATR FT-IR spectroscopy was done to establish the presence of charge-bearing groups in the membrane. The membranes were tested using single solute feed solutions of NaCl, Na2SO4, CaCl2, and MgSO4. Positive charges on the membranes were estimated in terms of their ion-exchange capacities (IEC). The values were also correlated to the solute-rejection properties of the membranes.