Abstract: To observe the pharmacokinetic and tissue-distribution characters of 5-flourouracil magnetic albumin deuto-microsphere (5-Fu-MAD) in normal and tumor-bearing mice, HPLC method for the determination of 5-Fu in plasma and tissues was established and applied to determine 5-Fu in mouse plasma and tissue samples. A Flame atomic absorption spectrometer was used to detect the iron concentration in mouse tissue. Plasma concentration-time curves of free 5-Fu, 5-Fu-MAD and 5-Fu-MAD plus the magnetic frame (MF) conformed to two compartment model of first order absorption and they had C_maxof 34.9, 7.95 and 5.97 mg·L^-1; T_1/2(Ke) of 22.26, 76.0 and 124.6 min, v_d of 3.28, 30.7 and 66.1 L·kg; AUC_0-T of 233.9, 78.3 and 50.2 mg·min·L^-1; AUC_0-∞ of 237.2, 89.3 and 68.1 mg·min·L^-1, respectively. The distribution of 5-Fu and iron was the highest in the plenty blood perfusion organs like the liver, tumor, spleen and lung, while lower in the kidney and heart and lowest in brain and muscle. The tissue distribution of muscle and tumor increased significantly when a magnetic frame was inserted there. The pharmacokinetics and tissue distribution of 5-Fu-MAD exhibited sustained-release and target characteristics.