A textile having excellent water- and oil-repellency can be obtained by a method of preparing a treated textile, having steps of: (1) preparing a treatment liquid comprising a water- and oil-repellent agent, (2) adjusting pH of the treatment liquid to at most 7, preferably at most 3, (3) applying the treatment liquid to a textile, (4) treating the textile with steam, and (5) washing the textile with water and dehydrating the textile, wherein the water- and oil-repellent agent is at least one fluorine-containing compound selected from the group consisting of a fluorine-containing polymer and a fluorine-containing low molecular weight compound, and the water- and oil-repellent agent or the treatment liquid contains an organic salt.