Heterogeneous systems using iron oxides with low-valent Fe(11) components, FeO and Fe3O4, were designed for controlled/living radical polymerization of styrene and methyl methacrylate. The polymerizations with FeO in conjunction with an alkyl halide initiator bearing a C-Br bond such as ethyl alpha-bromophenylacetate proceeded in controlled fashions in the solvent mixtures of N,N-dimethylformamide/toluene or acetonitrile/toluene to yield polymers with predetermined molecular weights. The controllability of the reactions was improved upon the addition of n-Bu4NBr to give polymers bearing theoretical M,, values and narrower molecular weight distributions. The polymerizations also proceeded using magnetic Fe3O4 or zerovalent Fe(0), although the controllability was inferior to FeO. The heterogeneous catalytic mechanisms using FeO were suggested by the effect of stirring on the reaction rate and some other polymerization results.