In a stirred batch reaction, Fe(phen) 3 2ϩ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate-driven oscillating reaction with ethyl hydrogen malonate [CH 2 COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N 2 atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen) 3 3ϩ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) Ͼ Ce(IV) Ͼ Ͼ Fe(phen) 3 3ϩ , which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen) 3 3ϩ ion. No good oscillations were observed for the BrO 3--CH 2 (COOEt) 2 reaction catalyzed by Ce(III), Mn(II), or Fe(phen) 3 2ϩ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR') with Ce(IV), Mn(III), or Fe(phen) 3 3ϩ ion is also presented.