The emulsifier-free emulsion polymerization of methyl methacrylate (MMA) was studied using sodium bisulfite as initiator in the absence and presence of a new organic chelating agent, N,N-dioxalyl p-amino benzoyl N,N-dioxalyl urea, and its iron (II) and (III) complexes. The organic ligand with free carboxyl groups has a retarding effect on the polymerization reaction while its iron complexes have a catalytic effect. The mechanisms of the catalytic effect of iron complexes or the inhibition mechanism of the organic ligand are discussed. The effect of pH values on the polymerization processes was also investigated. The apparent energy of activation was found to be 4.99 x 10(4) J/mol, 6.38 x 10(4) J/mol, 4.46 x 10(4) J/mol, and 3.72 x 10(4) J/mol in the absence and in the presence of 0.5 g of ligand and 0.1 g of its Fe (II) and (III) complexes, respectively.