Provided are a diketopiperazine mixture suitable for mixing with a food or drink and a method for producing the mixture. High-temperature and high-pressure treatment of plant peptides in a liquid allows production of a plant extract containing a high concentration of diketopiperazines including cyclo-leucyl-leucine and cyclo-leucyl-phenylalanine. The present invention can provide diketopiperazines having excellent flavor derived from a plant natural product and can produce a food or drink provided with the functions of the diketopiperazines by directly mixing the diketopiperazines with the food or drink.
