The change of lactic acid bacterial flora in kimoto (the traditional starter for sake brewing) was monitored, and the transition of the predominant microflora from Leuconostoc mesenteroidesto Lactobacillus sakei was confirmed. To clarify the cause of the transition of lactic acid bacteria in kimoto, we investigated growth factors for L.sakei. When L.mesenteroides and L.sakei were mixed-cultured in a GPY medium, L.sakei showed poor growth. However, when rice koji was supplemented, the growth of L.sakei increased remarkably. On the other hand, in the growth period of L.sakei in kimoto, the essential amino acids for L.sakei, arginine and asparagine disappeared in the supernatant. Approximately 0.1mM arginine and 1mM asparagine were required respectively for the sufficient growth of L.sakei. Sufficient amounts of arginine for the growth of L.sakei were liberated from raw materials in kimoto, while free asparagine was not sufficiently liberated, and it was considered that peptide-forming asparagine mainly contributed to the growth of L.sakei. Furthermore, L.sakei mutant defective in peptide utilization did not increase so much as the parental strain in kimoto. This suggests that the supply of peptide is important for the growth of L.sakei in kimoto.