A method is provided for preparing mixed greens. Greens are immersed in an aqueous solution containing phosphoric acid, calcium chloride and a natural antibiotic, dewatered from their surfaces, cooked and mixed in predetermined amounts. Following the application of a seasoning solution containing an organic acid and a natural antibiotic thereto, the mixed greens are vacuum packed and thermally sterilized. The mixed greens prepared according to the method can preserve their fresh texture senses for a long period of time.