GP11 had been reported to have effectively anti-tumor activity by improving the immune function in our previous study. To avoid drawbacks of the 5-Fu, GP11 in combinationwith 5-Fuwas investigated in this study. The results demonstrated that such synergism displayed enhance the anti-tumor activity of 5-Fu. Additionally, a strength effectwas also observed in regulating immune function of GP11 and 5-Fu simultaneous administration, such as enhancing seruminterleukin-2 (IL-2) and tumor necrosis factor-alpha (TNF-α) secretion, and increasing immune organs weights. Moreover, GP11 could improve the haematological and biochemical parameters deterioration, superoxide dismutase (SOD) activities reduction and malondialdehyde (MDA) levels enhancement in non-immune organs induced by 5-Fu. All these results illustrated that GP11 exhibited attenuated and synergized effect on 5-Fu by improving the immune function. It could be developed as an auxiliary preparation for chemotherapeutic drugs.