This paper focuses on the effects of the addition of fluorine-containing graft or block copolymer additives composed of 1H,1H,2H,2H-heptadecafluorodecyl acylate (perfluoroalkyl acylate, PFA) and poly(dimethylsiloxane) macromonomer (PDMS) or PDMS macro-azo-initiator to a microphase-separated membrane consisting of PDMS and poly(methyl methacrylate) (PMMA) on the benzene/water selectivity for an aqueous dilute benzene solution during pervaporation and the surface characteristics and structures of the surface- modified PMMA/PDMS membranes. The addition of the fluorine-containing copolymer additives, PFA-g-PDMS and PFA-b-PDMS, to a PMMA-g-PDMS membrane yielded hydrophobic surfaces at the air side of surface-modified membranes due to the localization of their additives on the air-side surface of these membranes. The addition of a small amount of the PFA-g-PDMS and PFA-b-PDMS enhanced both the benzene/water selectivity and the permeability for an aqueous dilute benzene solution during pervaporation because of the formation of their hydrophobic surfaces and the existence of the microphase-separated structures with a continuous PDMS phase in the inner of these membranes. When larger amounts of the PFA-g-PDMS and PFA-b-PDMS were added to a PMMA/PDMS, the latter additive could keep the microphase-separated structures with a continuous PDMS phase, but the former did not. The relationship between the permeation and separation characteristics for the removal of benzene from an aqueous benzene solution and the structures the PMMA-g-PDMS membranes surface-modified with PFA-g-PDMS and PFA-b-PDMS as fluorine-containing polymer additives is discussed in detail.