Abstract: Three series (a,b,c) of polyacrylic acid copolymers were parallel synthesized by using bio-reagent potassium phosphoenolpyruvate (PEPK) and acrylic acid (AA) as monomer in mild aqueous solution with Na2S2O8-Na2S2O5 as redox initiating system. The chemical structures of the PEPK-AA copolymers were determined by FT-IR, 13C-NMR and the molecular weight measurment. The PEPK-AA copolymers were characterized by TGA measurement, and the results indicate that the thermal stability of the copolymer was increased with the increasing of amount of PEPK component.