Abstract: 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 a method for efficiently extracting an oil-soluble substance from an object to be treated that contains water and the oil-soluble substance. 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 by mixing the object to be treated containing water or water and the oil-soluble substance with an oil at a temperature that is lower than the boiling point of water, at which temperature the oil is a liquid.