Reversed micelles have merited attention as a medium for carrying out enzyme-catalyzed reactions because of their interesting properties as hosts for biocatalysis. In order to understand the function of enzymes in these systems, it is necessary to know certain fundamental physicochemical properties of the micelles and how they interact. To date, the majority of characterization studies have been on ionic surfactant mixtures, in spite of the generally accepted notion that these systems can have deleterious effects on solubilized enzymes. Poly(oxyethylene) sorbitan trioleate (Tween 85) is a nonionic surfactant which forms reversed micelles in hexane using isopropyl alcohol or ethylene glycol as a cosurfactant. Tween 85 is completely biodegradable and can solubilize larger volumes of water that many other ionic or nonionic surfactants. Characterization studies on reversed micelles of Tween 85 are presented in this paper, including dynamic light scattering, viscometry, and conductivity. Micelle sizes have been determined at different water contents, along with intermicellar interactions.