The cell volume changes of Lactobacillus casei YIT 9018 in TGY broth in which glucose was replaced with fructose, galactose, maltose, lactose or surcose have been studied during 72 hours of cultivation at 37℃, and the effects of concentration of each saccharides were also studied in TGY broth. 1. Glucose, fructose and galctose were most effective for the cell volume increase of L. casei YIT 9018 in TGY broth containing 0.9% of each sugar while maltose, sucrose or lactose were not so effective for the increase of the cell volume. But these monosaccharides had not improved the cell volume when TGY broth contained only 0.3% sugars. 2. The cell volume of L. casei YIT 9018 reached maximum in 24 hours of cultivation in TGY broth containing monosaccharides and kept the cell volume for a while with only a slight decrease, but the cell volume decreased rapidly after 16 hours of cultivation in TGY broth containing disaccharides. 3. High concentration of glucose, including fructose and galactose, gave bigger cell size of L. casei YIT 9018 even after 72 hours than in low glucose TGY broth. The cell volume of L. casei YIT 9018, however, was not affected by supplementing disaccharides up to 0.9%. 4. At low concentrations of sugars, the monosaccharides may be better energy sources but at higher concentrations the sugar differences become narrower for the efficient growth in cell number and in cell viability of Lactobacillus casei YIT 9018 although the monosaccharides are better for bigger cell volume.