The rate constants for naphthalene entering and exiting from a micelle (k(+) and k(-), repectively) have been determined by the fluorescence quenching method for 1-dodecanesulfonic acid (DSA) and sodium 1-decanesulfonate (SDeSo) micellar solutions at 308.2 K. The first stepwise association constant ((K) over bar (1)) has been determined from the plots of maximum additive concentrations for each surfactant solution to obtain a ratio of the k(+) to k(-). The k(-) value for DSA has been found to be much smaller than the one for SDeSo, although the k(+) value for DSA has been found to be almost the same for both systems. This indicates that hydrophobic interaction between micelles and naphthalene dictates only in the case where the probe exits into intermicellar bulk solution.