PURPOSE: To provide a NATTO (fermented soybean) yogurt free from the smell of NATTO, takable easily, and having the activity of Bacillus natto, by inoculating Bacillus natto in soya milk prepared from soybean, and fermenting the milk.

CONSTITUTION: A large amount of soya milk prepared from soybean is put into a container, inoculated with Bacillus natto, cooled to the liquid temperature of 42W43°C, transferred to a chamber controlled at 42W43°C and fermented for 16W18hr. Since the liquid temperature is liable to increase rapidly at the latter half of the fermentation process, the room temperature is lowered to keep the liquid temperature at 42W43°C. The soya milk is converted to a complete NATTO yogurt free from the smell of NATTO, takable easily and having the activity of Bacillus natto.