Micellar-enhanced ultrafiltration was performed to remove an organic compound of low molecular weight such as tert-butyl phenol(TBP) from aqueous solution. The surfactant used here was cetyltrimethylammonium bromide(CTAB) and sodium salicylate(NaSal) was added to enhance the rejection efficiency. By using batch type ultrafiltration cell, the effects of the additive NaSal concentration in the retentate were investigated on the rejection efficiencies of TBP in terms of the molecular weight cut-offs or the membrane and molar ratios or NaSal, CTAB and TBP. When CTAB was added to the solution at concentrations well above its critical micelle concentration, the surfactant formed micelles and TBP molecules were dissolved into the micelle. And then, the micellar solution was forced to pass through an ultrafiltration membrane of which pore size was smaller than the micelle size. In ultrafiltration process, the micelle which contained TBP was rejected by the membrane. Thus, very little amounts of CTAB and TBP were contained in the permeate. As the filtration of the micellar solution proceeded, not only the solution viscosity was rapidly increased but the gel layer of highly concentrated CTAB was formed on the membrane surface. Consequently, the flux was reduced considerably. The results showed that, for a given molar ratio of NaSal to CTAB, there existed a critical concentration of NaSal, above which the flux was declined rapidly and the solution exhibited a remarkable viscoelasticity. However, below the critical concentration of Nasal, the rejection efficiencies of TBP were maintained above 98% due to the transition of micellar structure from spherical to worm-like networked micelle.