Production of yeast diet has been carried out in batch fermenters under optimum culture conditions. The fermentation of Candida utilis on a $2\%$ complex medium resulted in 1.22 g/L/h productivity and $65 imes10^8$ viable cells/ml, and the addition of $15{mu}M$ zinc to the medium increased both the productivity and the number of viable cells just a little more. In the case of the fermentation of Kluyveromyces fragilis, the highest value of the biomass productivity, 1.94 g/L/h, was obtained on a $2.5\%$ fructose medium with $70 imes10^8$ viable cells/ml, and $1\%$ peptone was found to be a growth factor in this fermentation. When $3.5\%$ NaCl was added to the given medium, both the biomass productivity and the number of viable cells decreased significantly in each fermentation, but this may be considered to preserve yeast diet long without osmotic lysis.