Abstract: The preparation of radioiodinated gambogic acid and its cell uptake in MCF-7 and biodistribution in mice were investigated. Gambogic acid was labeled with ¹³¹I using hydrogen peroxide.　The radiolabeled compound was characterized by polyamide TLC, in which the substratum of V(trichoromethane )∶V( methanol ) =40∶1 was used as developing agent. The uptake of ¹³¹Igambogic acid in cancer cells was measured. Biodistribution studies were carried out in KM mice. At different time after radiopharmaceutical i.v. administration (185 kBq ¹³¹Igambogic acid /mouse), the animals were sacrificed. Blood samples and the tissues of interested were collected, weighted and counted. The percent injected dose per gram (%ID/g) was calculated for each sample. The labeling yield of ¹³¹Igambogic acid is 86% and its radiochemistry purity are 97.2%, 95.4%, and 93.3% at 1, 4, and 20 d, respectively. The uptake of ¹³¹Igambogic acid in MCF-7 shows markedly higher compared with Na¹³¹I（P<0.01）.The in vivo biodistribution in mice indicates that ¹³¹I gambogic acid is mainly uptaked in liver, kidney, and intestines. The radioactivity in thyroid increases with time. ¹³¹Igambogic acid is stable and is markedly uptaked in cancer cells MCF-7. In mice, it is mainly metabolized by liver and excreted through kidney.