Horseradish peroxidase-mediated polymerization of styrene at ambient temperature is reported. Molecular weight and yield of polystyrene were influenced by solvent, concentration of hydrogen peroxide, and initiator (beta -diketones, coumarin). THF:H2O (v/v) and hydrogen peroxide (0.082 mol/L) provided maximum yield of polymer (21.2% weight conversion of styrene to polystyrene) with 2,4-pentanedione as initiator. 1,3-Cyclopentanedione and dibenzoylmethane as initiators resulted in higher yield of polymer (similar to 60%) and a higher molecular weight (M-n = 96 504, polydispersity = 2.16), respectively. This enzymatic strategy was also used for the synthesis of polymers from styrene derivatives, 4-methylstyrene and 2-vinylnaphthalene, the latter resulting in a >90% yield of polymer. The presence of the initiators in the polymer chains is reported.