In the brewing of sake, there are two typical procedures of making seed mash, called ki-moto type ( ki-moto and yamahai-moto ) and sokujo-moto .Effects of amino acids and organic acids on alcohol fermentation and on the viability of yeast during resting period ( karashi ) in yamahai-moto and sokujo-moto were examined, and following results were obtained: (1) The number of living yeast cells was reduced faster in sokujo-moto than in yamahai-moto during resting period, as is generally accepted. (2) Amino acids had the tendency to reduce alcohol fermentation by yeast in the presence of alcohol.Their effects were related to the relative amount of amino acids and alcohol concentrations, that is, the more amount of amino acids were present, the less alcohol was produced in usual alcohol concentration of the seed mash. (3) Organic acids had also the same effect as amino acids on alcohol fermentation during resting period. (4) The amounts of amino acids and organic acids contained in yamahai-moto were about 3 times and 1.5 times as much, respectively, as those in sokujo-moto .This difference in the amounts of amino acids and organic acids between both seed mashes was considered to be a reason why yeasts in yamahai-moto were protected from damage by high alcohol concentration, resulting in maintaining their number of living cells during resting period.