PURPOSE: To prepare a soybean milk having improved operability and water retaining property, by adding a rapid acting coagulating agent e.g. magnesium chloride, and a monovalent chloride, e.g. potassium chloride in a specific amount or more in a relatively almost saturated solution state to a soybean milk, and coagulating the soybean milk.

CONSTITUTION: 100pts.wt. rapid acting bivalent coagulating agent, e.g. magnesium chloride, and 20pts.wt. or more bivalent chloride, e.g. potassium chloride, in a solution of high concentration of 60% or more based on the saturated solution value as a slurry are added to a soybean milk. The method is characterized as follows: The specific amount of the monovalent chloride to be added and the specific concentration of the mixed solution thereof increase the buffering ability, and the aimed bean curd having improved water retaining property is obtained with good operability.