Cyclization of 2-((3-halopropyl)oxy)phenoxide ion (halo = Br, I; PhBr7 and PhI7, respectively) in micelles is a model for S(N)2 reactions of nucleophilic anions at micelle-water interfaces. Sulfobetaine micelles of dodecyldimethylammoniopropanesulfonate (C12H25N+ (CH3)(2)(CH2)(3)SO3-, SB3-12) modestly increase rates of cyclization of PhBr7 and PhI7, and the effect is larger for the latter. The relative rate constants k(I)/k(Br) are indicators of medium polarity and their values indicate that the surface polarity of micellized SB3-12 is slightly lower than that of a trimethylammonium micelle and significantly lower than that of water. Changes in H-1 chemical shifts of SB3-12 show that the micellar rate effects are not due ta-changes in micellar structure. Nonionic micelles of polyoxyethylene(23) dodecyl ether (C12H25(OCH2CH2)(23)OH, Brij 35) modestly speed up cyclization, but reaction appears to be in the water-rich palisade layer of the micelle in conditions such that the distinction between aqueous and micellar pseudophases is uncertain.