The surface-selectivity of photo-grafting has been used as a crucial parameter to evaluate the 'grafting-from' efficiency of the synergist immobilization method developed in our recent work. The factors that affect surface-selectivity of photo-grafting have been further investigated. It was shown that the competition of solvent with the membrane surface towards the generation of starter radicals led to a decrease in the degree of grafting and surface-selectivity of photo-grafting. High UV intensity made the functionalization mechanism more complicated, due to the generation of a new type of starter radical at the membrane surface with immobilized synergist in the absence of BP and because it could lead to crosslinking in the grafted layer. An appropriately low photo-initiator concn. was also required in order to achieve the ideal surface-selectivity of photo-grafting. In addn., this method has been successfully applied to the track-etched PET membranes. Pore size distributions as well as ethanol and water permeability of the membranes were used to retrieve information about the effective thickness of the grafted polymer layers.