In the oligomerization of p-aminophenol by the catalytic action of Fe-EDTA complex in the aqueous medium, the mixed complex intermediate, Fe-EDTA-M type, is considered to be formed, from which active radicals of the monomer are produced. In this system, polymerization is presumed to proceed as follows: Free radical formation ${ o}$ Coupling ${ o}$ Activation ${ o}$ Coupling, and so on. In this study, the form of the monomer and coordination state in the mixed complex, the catalytic action of Fe-EDTA the complex, the reaction mechanism, and the structure of the oligomers are discussed.