Abstract: FCA (Freund's Complete Adjuvant,FCA)is usually used to entrap antigen to immunize animal， We entrapped 5-Fu with FCA to slow their release in vivo and by means of this to reduce their side effects and to augment their antitumor effects. We called these FCA entrapped 5-Fu,5-Fu-FCA. The results showed that:the average survival time of 5180, EAC and H22 tumor bearing mice treated with 5-Fu was 18. 3±1. 6, 17. 9±1. 9 and 19. 1±3. 6 days respectively, none of them were cured， while that of S-Fu-FCA treated groups was 48. 3±21. 1，30. 6±2. 3 and 33. 4±21. 6 days and 3/8, 2/8, Z/8 of the tumor bearing mice cured respectively (vs S-Fu treated groups，Ｐ＜0. 0001). We conclude that:(1) the adverse effects of 5-Fu could be significantly reduced by means of FCAentrapping; (2)the antitumor effects of 5-Fu could be augmented by means of FCA entrapping.