Abstract:The viable count of Enterococcus faecium was the key factor to functionality of fermented feed. To get the highest viable count of E. faecium during the fermentation period， the effects of the four different character－ istics of yeast extracts on that was discussed. With the method of single factor experiment， the viable count of E. faecium was determined by shake-flask cultures using yeast extract as a sole nitrogen source. Then based on the detecting results of yeast extract， the crucial factors of effect on the viable count could be finding out. Experi－ ments have indicated that yeast extract which provides growth factors and microelement has significant impact on the cellular activity of E. faecium， and the initial concentration of free nucleotides in the media was the im－ portant factor that affects the vitality of E. faecium. By adding a certain amount of free nucleotides， and incubat－ ing under anaerobic conditions for 12 hours， the maximum number of viable count wasattained 176×108 CFU/mL， which was nearly 40 % higher than the maximum number of viable count before the optimization process. The conclusion was that the viable count of E. faecium could be improved by added a certain amount of free nu－ cleotides in the initial media， and it was applied to the industrialized production of probiotic strains used in fer－ mented feed production.