Gamma aminobutyric acid (GABA) is a non-protein bioactive compound that can be effective in controlling many diseases such as Alzheimerchrs, hypertension, stress, etc. The main stimulus for the production of GABA is the enzyme glutamic acid decarboxylase (GAD), which is highly active in lactic acid bacteria. Also, the presence of monosodium glutamate (MSG) can act as a substrate for this enzyme and increase its activity. In this study, the production potential of gamma aminobutyric acid by Lactobacillus brevis PML1 in MRS medium was investigated. In order to optimize the fermentation process, culture medium containing MSG (1, 3 and 5%) was examined at 24, 48 and 72 hours.  after fermentation, thin layer chromatography method was used to identify GABA produced by bacteria. Spectrophotometric method was used to quantify the bands in thin layer chromatography. The results of studies at the level of 95% significance showed that the optimal treatment included a culture medium containing 5% monosodium glutamate and a time of 72 hours at 37 ° C, in which the amount of GABA production was approximately 300 ppm; Therefore, the desired strain not only has the potential to produce gamma aminobutyric acid under normal conditions (control sample) but also by adding different percentages of monosodium glutamate to the culture medium, the amount of this production can be increased.