Abstract: The mechanism of 732 cation-exchange resins on the promotion of whole cells'glutamate decarboxylase (GAD, EC4.1.1.15) activity of Enterococcus faecium was investigated from the effects of 732 cation-exchange resins on the pH value of the whole cells conversion system, product and substrate effect by comparative analysis of whole cells and purified enzymes.The results indicated that the activity of whole cells'GAD was inhibited by γ-aminobutyric acid (GABA), and no inhibition was observed by L-glutamic acid (L-Glu).On the contrary, the activity of whole cells'GAD could reach its maximum only when the concentration of L-Glu was more than 200 mmol/L.Under the conditions of pH4.2 to 5.8, GABA was more easily dissociate to cations than L-Glu, and could replace the L-Glu and H⁺ that combined to the resins from the equilibrium liquid, which could supplement the free L-Glu, decrease the free GABA, and regulated the pH of the reaction system. These results suggested, the mechanism of 732 cation-exchange resins on the activity promotion of whole cells'GAD of Enterococcus faecium was via increased free substrate concentration, reduced free product concentration and regulated the pH of the reaction system through released H⁺ and L-Glu, and adsorbed GABA by ion exchange, which could enlarge the concentration difference between intracellular and extracellular, overcome mass transfer barriers and speed up the transport of substances inside and outside cells, thus improving the apparent activity of whole cells'GAD.