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Background and Objective: Production of gamma-aminobutyric acid has recently much interested because of its benefits for health. The objective of this study was to optimize y-aminobutyric acid production by a novel identified Lactiplantibacillus pentosus isolated from a fermented shrimp paste of ruoc. Material and Methods: A species of lactic acid bacterial was isolated from 'ruoc', a highsalt fermented shrimp paste and identified using matrix-assisted laser desorption/ionizationtime of flight mass spectrometry. The gamma-aminobutyric acid production was optimized using various culture conditions (initial cell density from 5 x 10(5) to 5 x 10(7) CFU ml(-1), monosodium glutamate concentration of 0.5-2% (w v(-1)), initial pH of 4-9, incubation temperature of 30-50 degrees C and incubation time of 24-120 h) with one-factor-at-a-time approach. Results and Conclusion: Of 20 lactic acid bacteria isolated from 'ruoc', four isolates of R1, R3, R12 and R13 produced significant quantities of gamma-aminobutyric acid. Isolate R13 produced the highest gamma-aminobutyric acid quantity, identified as Lactiplantibacillus pentosus using matrix-assisted laser desorption/ionization-time of flight mass spectrometry. A culture media optimization study was carried out for Lactiplantibacillus pentosus R13 to improve its gamma-aminobutyric acid yield. Results showed that at optimal conditions of 1.5% monosodium glutamate (w v(-1)), initial pH of 7, initial cell density of 5 x 10(6) CFU ml(-1), cultivation temperature of 45 degrees C and fermentation time of 96 h, Lactiplantibacillus pentosus R13 produced 23.34 mM +/- 0.11 of gamma-aminobutyric acid. In conclusion, gamma-aminobutyric acid production by this isolate was verified to be heavily dependent on monosodium glutamate concentration, initial cell density, initial pH, incubation temperature and fermentation time.