The growth of Lactobaillus brevis NCL912,a γ-aminobutyric acid high-yielding strain,in acid environment and its acid tolerance in extreme acid environment(pH 2.0) were investigated in this paper.Meanwhile,the comparision of the growth,acid resistance,the yield of γ-aminobutyric acid and glutamate decarboxylase activity were determined in the media with and without the addition of L-glutamate sodium(L-MSG).The results showed that Lactobaillus brevis NCL912 could grow at pH>3.0,grow well at pH 5.0,and could survive for more than four hours at pH 2.0.The addition of L-MSG can enhance the growth of the strain.L-MSG was converted completely to γ-aminobutyric acid at pH4.0.In addition,the survival percentage(%) and the glutamate decarboxylase activity in the media with and without L-MSG were significantly different(P<0.05).The survival percentage(%) and the glutamate decarboxylase activity were better in the media with L-MSG.It was implied that the acid resistance of Lactobaillus brevis NCL912 was related to glutamate-γ-aminobutyric acid antiporter system.