We studied on the effect of adding egg white with acid on gustatory free amino acid in the soup stock of dried shiitake mushrooms and on sensory evaluation of the soup stock. The following results were obtained. 1) The amount of gustatory free amino acid in the soup stock increased more than that in original soup stock by adding 3 or 5 % egg white to the soup stock adjusted to pH 5.2 or 4.6. The rate of increase was 1.3-1.5 times higher than that in the original, when 3% egg white was added to the soup stock adjusted to pH 4.6 and boiled for 30 min, and when 5% egg white was added to that and boiled for 10 or 15 min. 2) On the sensory evaluation, the score of intensity of color and harshness of the soup stock became lower and the score of impression for color of that became higher by adding egg white with acid. The score of intensity of umami, sweetness and fullness of the soup stock adjusted to pH 4.6 and boiled for 10 min after adding 3% egg white was higher than that of the other samples and the original.