The nitrosation reaction of benzoylacetone (1-phenyl-1,3-butadione) by nitrous acid in an aqueous acid medium is studied in the presence of anionic and cationic micelles. The reaction involves enolization of the ketone, followed by electrophilic nitrosation of the enol. The presence of micelles strongly modifies the keto-enol equilibrium of beta-dicarbonyl compounds, like benzoylacetone, in such a way that the enol percentage increases with the surfactant concentration The increasing enol amount with surfactant concentration is quantitatively evaluated by studying the effect of surfactant addition on the UV-vis spectra of benzoylacetone; the results are used to explain the kinetic data. The addition of hydrogen dodecyl sulfate (HDS) to the reaction mixture increases the nitrosation reaction rate continuously until levels off at high HDS concentrations. In the presence of sodium dodecyl sulfate (SDS), the observed rate constant increases at low surfactant concentrations, passes through a maximum, and decreases at still higher SDS concentrations. The observed kinetic effects in the presence of the cationic surfactants tetradecyltrimethylammonium salts of Cl-, Br-, NO3-, and SCN-anions, in general TTAX (with X being Cl-, Br-, NO3-, or SCN-), depend on the nature of the micellar counterion; for example, the addition of TTANO(3) decreases the reaction rate for the entire concentration range investigated, while the presence of TTASCN calatyzes the reaction. The varying micellar effects are quantitatively interpreted on the basis of reaction mechanisms, with consideration given to the possible nitrosating agent in every case.