Abstract: A strain of Lactobacillus was isolated from the homemade yogurt in Inner Mongolia． Through physiological，biochemical and morphological identifications and 16S rDNA homology analysis，the strain was known to be Lactobacillus delbrueckii DMLD-H1． The biological characteristics of the strain were studied to clarify its gastrointestinal tolerance，antibacterial effect and probiotic characteristics． The safety of the strain was evaluated through hemolytic experiment and acute toxicity test． The fermentation medium of the strain was optimized by response surface methodology． The results show that Lactobacillus delbrueckii DMLD-H1 grow rapidly at the optimum temperature of 37 ℃ and pH value ranging from 3. 0 ～ 7. 0． The blood agar plate study shows that the strain has no hemolytic activity． The acute toxicity test indicates that Lactobacillus delbrueckii DMLD-H1 has no acute oral toxicity to mice． Thus the strain has the characteristics of edible bacteria． After incubation for 3 h in artificial gastric and intestinal juice whose pH value is 3. 0 ～ 4. 0，the survival rate of the strain is above 85% ，with good tolerance． Its fermentation products have inhibitory effects on both Escherichia coli and Staphylococcus aureus，indicating that Lactobacillus delbrueckii DMLD-H1 has potential probiotic properties． When the best components of the fermentation medium are optimized as follows: oligo-fructose content 20. 2g /L，bacteriological peptone content 19. 7g /L and magnesium sulfate content 0. 596 g /L，the concentration of viable bacteria of Lactobacillus delbrueckii DMLD-H1 is 1. 32 ×109 CFU/mL． Under this condition，the fitting rate between the above-mentioned concentration and the measured value is 98. 48% ，indicating that after the optimization of the medium，the model can well predict the bacteria's growth characteristics．

Key words: Lactobacillus delbrueckii, biological characteristics, fermentation medium optimization