Nitrophenols are common organic pollutants that enter the environment during the manufacture and processing of a variety of industrial products. The removal of 4-nitrophenol (4NP) from aqueous solutions by emulsion liquid membranes using the type I facilitated transport mechanism is investigated in this paper. The liquid membrane consisted of kerosene as the organic diluent, sorbitan monooleate as the emulsifying agent and sodium hydroxide as the stripping agent. The most important operational variables governing the emulsion stability and the 4NP removal process--such as the stripper agent and surfactant concentrations, the volume ratios of membrane phase/internal phase and emulsion phase/feed phase and stirring speed - were studied and the optimal conditions of the removal process were experimentally determined. Apparent initial permeabilities of the transport process in the different operational conditions were also obtained. Ninety-eight per cent of4NP was removed in 10 minutes and an apparent initial permeability of 1.2986 min(-1) was obtained in those optimal conditions.