The effect of K_La(Oxygen Transfer Coefficient) and substrate feeding policy on the optimum cell yield and productivity was investigated in the baker's yeast fed-batch cultivation. K_La was measured at various agitation speed (100 to 600 rpm) and aeration rate (1.0, 1.5, 2.0 vvm), and the cell yield and productivity of fed-batch cultivation was determined at each agitation speeds (300 to 600 rpm) and constant aeration rate (1.5 vvm). K_La value was increased proportionally with increasing agitation speeds and aeration. Substrate feeding pattern was optimum in sigmoidal feeding. The optimum total fed-sugar and productivity was largely dependent on the K_La and did not change at above 500 rpm, and the cell yield was decreased gradually as the K_La increased. It is considered that the increase of the accumulation of inhibitory substances in the molasses by the increase of molasses feeding, the accumulation of fermentation metabolites, the viscosity and cell concentration of fermentation broth, and so forth was decreased the cell growth rate and oxygen transfer rate. So, the optimum operation condition of this fermentor was estimated to near 500 to 600 rpm.