Abstract: The V. harveyi bioassay method was carried out to explore that 8 lactic acid bacteria which isolated from koumiss of Ximeng region in Inner Mongolia produced the quorum-sensing signal autoinducer-2(AI-2)and found the production pattern. AI-2 high-producing strain was screened for molecular biological identification and relationship between AI-2 and bacterial density was further studied. The results showed that all strains could produce AI-2,among of which the ability of AI-2 production of strain 2-1 was superior(p<0.05) and identified as a Lactobacillus fermentum. The concentration of AI-2 increased with bacterial density and the largest amount of AI-2 was observed in the early stationary phase in the culture of strain 2-1.