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 antituor effects.We called these FCA entrapped 5-Fu, 5- Fu-FCA.The average rate of entrapping 5-Fu by FCA is 84. 5%.The experiment showed that 5- Fu-FCA had a slow release of 5-Fu in vitro and in vivo.The proliferation inhibition rate of H22 tumorcells by higher concentration of 5-Fu (200μg/ml,10min )was 34. 66±6.02,significantly higher than that by lower concentration (50μg/ml)of 5-Fu and the same time(13.46±11.54,P0.01),but lower than that by lower concentration(50μg/ml) of 5-Fu and longer time(24h,61.35 ±7.18,P0.008).We conclude that:(1)the release of 5-Fu is markedly reduced in vivo by FCA entrapping;(2)lower concentration of 5-Fu aam longer time may have stronger antitumor effects.