The present invention relates to a method of treating leukemia using rice prolamin, and a pharmaceutical composition for treating leukemia, comprising an effective amount of rice prolamin together with one or more pharmaceutically acceptable carriers or excipients. For the treatment application, the rice prolamin can stimulate human peripheral blood mononuclear cell (PBMC) to produce cytokines, such as tumor necrosis factor-alpha, to inhibit growth of and induce differentiation of human leukemia U937 cells. The rice prolamin is gluten-free, thus will not trigger gastrointestinal allergic reaction.
