Abstract: The mechanism of reaction between rare earths (RE) and Chromazurol S (CAS) ,o-phenanthroline (o-phen.) in the presence of amphoteric active agent (DDMAA) has been studied spectrophotometrically.The results show that the maximum absorption is obtained at the point at which the concentration of DDMAA reached the CMC. Thus, it can be seen that the formation of micelles appears to have an important effect on complex reaction. The amphoteric active agent is in the form of cationic species which was proved by examining the electronic nature of DDMAAand the complex.The molar ratio of the four components in the complex is estimated to be Y:o-phen:CAS:DDMAA = 1:l:2:4 and the possible structure of the complex is proposed.