The compound 5-aminoquinoline (AQ) was treated with horseradish peroxidase (HRP) and H2O2 in a reaction medium containing a dioxane: phosphate buffer mixture (70:30). Products (OAQ) with a degree of polymerization ranging from 4 to 12 were obtained. H-1 NMR, FTIR, UV-vis, SEM, TG-DTA, DSC, XRD analysis, and conductivity measurements were conducted for characterization of OAQ. Compared with a monomer, OAQ showed higher thermal stability. After heating to 1000 degrees C, 46% of the initial weight of the OAQ remained. The antioxidant efficiencies of the monomer and oligomer were evaluated by the typical spectrophotometric method such as the bleaching of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. OAQ showed improved DPPH activity compared with the AQ monomer.