Electrophoretic light scattering measurements were performed for aqueous NaCl solutions of dodecyl-, tetradecyl-, and oleyldimethylamine oxides (C12DAO, C14DAO, and ODAO). Electrophoretic mobility for 0.1 M NaCl solutions of C14DAO changed from negative to positive, as degree of protonation was increased. NaCl solutions (0.03 M) of ODAO displayed similar behavior, and their positive mobility increased with degree of protonation. On the other hand, 0.05 M NaCl solutions Of C14DAO presented three kinds of electrophoretic mobility at approximately -2.5 x 10(-4), approximately 0, and approximately 2 x 10(-4) cm2 V-1 s-1 depending on degree of protonation, and there were transitions from negative to zero and from zero to positive at narrow degrees of protonation. A similar result was also obtained for 0.05 M NaCl solutions Of C12DAO. The electrophoretic mobility is related to the electrostatic potential of a micelle which is affected by degree of protonation of a micelle and counterion binding. Experimental results are qualitatively explained in relation to the variation of such parameters.