Abstract: In Lactobacillus plantarum KLDS1.0391 which can produce the bacteriocins, the effect of galactooligosaccharides ( GOS) which substituted for glucose in MRS media were studied in vitro fermentation. The titratable acidity, p H value and amounts of viable bacteria were determined during fermentation of 36 h at 37 ℃ in both of MRS and m MRS ( GOS substituted for glucose) . The contents of organic acids and bacteriocins were also determined at the cultivation of 28 h and 24 h respectively. The results showed that the p H value decreased rapidly with the cultivation and then changed sloely after cultivation of 12 h, and the growth-stimulating effect of galactooligosaccharides ( GOS) was significantly higher than that of glucose ( p < 0.05) , meanwhile the decline was slower.Moreover, the concentrations of organic acids and antimicrobial activity of the bacteriocins in m MRS were higher than that in MRS, and the main organic acids were lactate, acetate and propionate.