Abstract: The response reaction of Lactobacillus acidophilus cell on acid- stress through the related enzyme regulation in extremely acidic environment were studied. The result showed that the enzymatic activity of intracellular arginine deiminase of test strains,Lactobacillus acidophilus Ind- 1( La- XH1) and Lactobacillus acidophilus Lakcid( La- XH2),was increased to 4.55 μg / min·m L and 4.13 μg / min·m L respectively at p H1.5.The intracellular urease activity of La- XH1 and La- XH2 was 1.33 U and 1.26 U,which were increased slightly. By analyzing the enzyme activity related to proton pump,the result showed that the H+- ATPase activity of La- XH1 was increased with the decrease of p H,and enzyme activity was 5.49 μmol / min·L at p H1.5. However,the H+-ATPase activity of La- XH2 had no significant change,which indicated La- XH1 and La- XH2 had strain differences.Meanwhile,the enzyme activity of glutamate decarboxylase had an increasing tendency with the decrease of p H,and the enzyme activity of La- XH1 and La- XH2 was 0.336 mmol / h·L and 0.229 mmol / h·L respectively at p H1.5.The study indicated that Lactobacillus acidophilus could activate the enzyme activity related to improve its acid-resistant ability on acid- stress condition,in order to maintain the normal physiological function of cells in extreme environment.