The present invention suggests a method for treating a liquid food, which is suitable for efficiently and effectively decreasing the dissolved oxygen concentration in liquid foods having high foaming property and low defoaming property such as skim milk. The dissolved oxygen concentration of the liquid food is decreased by putting the liquid food into a decompression vessel while heating the liquid food to a temperature higher than or equal to the saturation temperature (boiling point) of the liquid food under the decompression atmosphere in the decompression vessel, or putting the liquid food into a decompression vessel while depressurizing the decompression vessel to a pressure lower than or equal to the saturation vapor pressure of the liquid food at the temperature of the liquid food.
