The ultrasonic absorption has been measured in aqueous solution of dodecyl pyridinium chloride (DPC) at $20^{circ}C$ over the frequency range of 0.1${sim}$90 Mc.The excess absorption was observed only in solutions in which the concentration was higher than the critical micellar concentration(cmc). The mechanism for this feature was attributed to the reaction $M_2;{ ightleftharpoons};M_1;＋;1.2Cl^-$ Where $M_2$ and $M_1$ and M1 are two types of micelle. The rate constants of the forward and the reverse reactions were $6.6{ imes}10^5 sec^{-1};and;2.7{ imes}10^11sec^{-1}mol^{-1.2}$respectively. Some kinetic charateristics including the free energy, enthalpy and entropy were calculated.