The invention relates to a preparation method of fermented milk, which comprises the steps that: at the beginning of fermentation, concentration of dissolved oxygen in raw material mixture of the fermented milk is reduced to 5ppm, and fermentation is performed at the temperature ranging from 30 to 39 DEG C or the addition amount of starter added to the mixture of the fermented milk is 25 to 50% of normal addition amount, and fermentation is performed at the temperature ranging from 38 to 46 DEG C.
