The hydrogen ion titration of long alkyl chain amine oxide micelles was carried out at various salt concentrations, C s , surfactant concentrations, C D , and temperatures T. The surfactants studied were alkyldimethylamine oxides (CnDAO) with hydrocarbon chain lengths of 10-16 (n = 10, 12, 14, and 16), and N, N-bis(2-hydroxyethyl)alkylamine oxide (CnDHEAO) with hydrocarbon chain lengths of 10-14 (n = 10, 12, and 14). The intrinsic dissociation constant exponents, pK M , of the micelle were greater than those of the monomer, pK 1 , for all systems examined. Thus, the introduction of electric charges is more favored on the micelle surface than to the monomer in solution. The values of pK M of CnDAO at 25 โข C in 0.1 M NaCl were dependent on the hydrocarbon chain length in the following order: C10 (5.5) < C12 (5.9) < C14 (6.3) โ C16 (45 โข C; 6.2). This order can be interpreted reasonably in terms of different curvatures of the micelles that are determined by the intrinsic packing parameter value modified by the proposed hydrogen bond between protonated and unprotonated species on the micelle surface. For CnDHEAO, we observed practically identical pK M values for different chain lengths. Comparing CnDAO with CnDHEAO with the same hydrocarbon chain length at the same C s and C D , pK M values for CnAO were greater than those for CnDHEAO. Values of pK M were independent of C s and C D examined for both CnDAO and CnDHEAO. Anomalous titration behavior in the low charge density region was attributed to inaccurate estimation for the blank titrations. The monomer concentrations in a range higher than critical micelle concentration (cmc) were evaluated from the hydrogen ion titration with the assumed Gibbs-Duhem relation. These values coincided with the cmc values for C10DAO and C12DHEAO.