Abstract: Objective To observe the immunoprophylaxis mechanism of mustard seed against colorectal cancer in rats induced by 1,2-dimethylhydrazine (DMH)．Methods Fourty-eight male Wistar mice with 5 weeks old were divided into 4 groups randomly and equally. The colorectal cancer model was induced by intraperitoneally injecting DMH. The lymphocyte cells were isolated and the rats were injected with oneto-one adoptive transfer strategy. After 32 weeks, the presence, number and size, occurrence rate, thymus and spleen index of colorectal tumor as well as the expression of CD4+T and CD8+T of spleen cells were observed. Results The colorectal cancer model was successfully induced by DMH in this experiment. No tumor was present in the control group. The total tumor incidence in DMH group was 91.7%. The tumor incidence in DMH combined with lymphocyte cells group and 7.5% MS group were 40% and 50% lower than that of DMH group respectively. The thymus and spleen index of 7.5% MS group and DMH combined with lymphocyte cells group were markedly large than that of DMH group(P<0.05). And the ratio of CD4+T and CD8+T was decreased (P<0.05). Conclusion MS could prevent colorectal cancer induced by DMH by strengthening organism immune system.