The purposes of the present invention are two provide a method for efficiently reducing water content of an object to be treated that contains water without requiring a high-temperature environment such as one exceeding the boiling point of water, and to provide another method for efficiently extracting an oil-soluble substance from an object to be treated that contains water and the oil-soluble substance, which comprises the same treatment steps as those in the above method for efficiently reducing water content. A method for reducing water content of an object to be treated and/or extracting an oil-soluble substance in the object to be treated into oil is performed, which method is characterized in that the object to be treated containing water or water and the oil-soluble substance is mixed with the oil at a temperature that is lower than the boiling point of water, at which temperature oil is liquid.
