The glutamic acid fermentation was carried out under different initial biotin concentration to investigate the effect of biotin on glutamic acid secretion.The results indicated that biotin concentration was the key factor to control glutamic acid secretion.The secretion of Glutamic acid was started when the concentration of biotin was within 1.97～2.29 μg/g DCW of "nominal biotin-limitation".The glutamic acid secretion was immediately terminated when 20μg/L biotin was supplemented during glutamic acid secretion.After that the intracellular glutamic acid began to increase which further indicated that glutamic acid secretion was controlled by biotin concentration.A new assumed secretion mode-"biotin concentration trigger secretion" was proposed through the comparison of intracellular and extracellular glutamic acid concentrations.