It is well known that lactic acid bacteria make an essential contribution to the good flavor and taste of bread, and that good sour bread could not be made in Japan, even when using imported commercial sour bread starters. To establish a new method of sour bread making and to maintain the quality and safety of the bread, pure cultures of brewing microorganisms and their mixtures were used to produce the sponge. As Lactobacillus sakei HM-3 has the ability to grow at 5°C in traditional and natural seed mashes of Japanese sake, it was used as the main strain because it was possible to obtain effective microbial and thermal control of the dough fermentation.A brewer's yeast, Saccharomyces cerevisiae ST-1, that has the ability to assimilate lactic acid and shows good fermentability was selected from the 36 industrial yeast strains tested for their ability to make good sour breads. The improved sour bread starter sponge, containing more free amino acids, could be obtained after 40 hrs fermentation at 10°C with the addition of L.sakei HM-3 and S.cerevisiae ST-1 cells at a ratio of 3 to 2.This improved starter makes it possible to make good sour bread.