In this communication, acrylamide (AM) polymerisation to poly(acrylamide) was initiated by horseradish peroxidase (HRP) and acetylacetone (ACAC) without hydrogen peroxide (H₂O₂). Electron spin resonance (ESR) spectroscopy showed that free radicals of ACAC and AM were present in the reaction. Gel Permeation Chromatography (GPC), FT-IR, ¹H-NMR and relative viscosity indicated that the product was PAM. Furthermore, the enzymatic cycling mechanism of the HRP–ACAC–H₂O₂ ternary system was also explained.