AIM:To prepare 5-FU sodium alginate(125)I bovine serum albumin nanoparticles (BSA NP), to determine the radioactive count in different organs of rats at different time points after oral administration of 5-FU (125)I sodium alginate-BSA NP and to calculate the kinetic parameters of its metabolism.METHODS:Emulsion solidification method was used to prepare 5-FU (125)I sodium alginate-BSA NP, and to determine its diameter under transmission electronic microscope (TEM). Then the rate of NP and external drug releasing velocity were measured. Radioactive counting in different organs of rats was made after oral administration of the NP by GAMA Counter, and the kinetic parameters of drug metabolism were calculated by handling the data with the two-department model.RESULTS:The average arithmatic diameter of the NP was 166nm ± 34nm, the rate of 5-FU was 32.8% and the cumulative external releasing ratio amounted to 84.0% within 72 hours. The NP was mainly distributed in the liver, spleen, lungs and kidneys after NP oral administration to rats. The micro-radioautographic experiment showed that NP was distributed in the Kupffers cells of liver, liver parenchymal cells and the phagocytes of spleen and lungs. The kinetic parameters of matabolism were: T(1/2) = 9.42h, C(max) = 2.45X10(7)Bq,T(max) = 2.18h, AUC = 148X10(9)Bq.CONCLUSION:NP is difficult to pass through the blood-cerebral barrier,and (125)I sodium alginate-BSA NP enters the body-circulation by gastroin testinal passage.