The effect of fluorination on the surface characteristics and water permeability of an isopore polycarbonate track etched membrane was examined. The membrane was fluorinated with gas mixtures containing fluorine and nitrogen of various composition under various pressure at room temperature for 3 minutes. The field emission scanning electron microscopy (FESEM) analysis showed that the shape of the membrane surface was not changed when it was fluorinated with a gas mixture at 1.5 bar which contained a low molar ratio of fluorine to nitrogen such as 1:30. Meanwhile, the membrane fluorinated with a mixture having a F₂ : N₂ ratio of 1:30 at 1.5 bar showed an improved water permeability almost twice higher than that the original membrane had. The membrane surface got to possess more hydrophilicity than the original one when it was mildly fluorinated at low pressure. However, it became hydrophobic when it was further fluorinated under higher pressure. X-ray photoelectron spectroscopy (XPS) analysis revealed that the penetration rate of fluorine into the membrane increased along with the increase of the partial pressure of fluorine and that the inner layer containing fluorine possessed more oxygen than that in the original membrane. The phenomenon that the membrane having hydrophobic surface showed high water permeability was due to the slip boundary condition in the pore surface where water droplets pass through hydrophobic pores more easily with less friction resistance than through hydrophilic pores.