The copolymerization behavior of the one-step direct polycondensation of 3,5-bis-(4-aminophenoxy)benzoic acid (AB(2) monomer) and 3-(4-aminophenoxy)benzoic acid (AB monomer) was investigated by IR and C-13 NMR measurements. IR measurements revealed that the content of the AB(2) units in the polymer was higher in the early stages of polymerization. C-13 NMR spectra of the polymers indicated that the number of dendritic units increased slowly with increasing reaction time. The stepwise copolymerization of the AB(2) and AB monomers was also carried out, and the structure was analyzed by C-13 NMR measurements. Copolymer synthesized stepwise by adding AB(2) monomer first (polymer II) had more dendritic units and less terminal units as compared with the one-step copolymer (polymer I). Copolymer synthesized stepwise by adding AB monomer first gave a resulting copolymer (polymer III) composed of long AB chains. The solubility of the stepwise copolymers was low, and the inherent viscosity was high in comparison with the one-step copolymer as a result of the difference in architecture of the copolymers.