Abstract: To investigate the relationship of anticancer effects, toxicity and dose, tumor syngeneic models were made from murine colorectal adenocarcinoma cell line CT26 derived from BALB/c mice. Mice were treated with various doses (10, 20, 30 and 50 mg/kg) of 5-fluorouracil (5-FU), and the indexes were analyzed, including the anti-tumorigenic effects, body mass and mortality of mice. The results showed that the efficacy and toxicity of 5-FU was closely related to the doses, and the proposal dose was 20-30 mg/kg which may be the optimal dose for drug research in tumor syngeneic model of mice.