Purpose: Idoxifene is currently entering phase Ⅱ clinical trials for the treatment of advanced breast cancer. The radiolabeled idoxifene using 123I provides an opportunity for clinical pharmacology with single photon emission computed tomography (SPECT). The purpose of this study was to prepare radiolabeled idoxifene using 123I and to determine its cell uptake of breast cancer cell line. Materials and Methods: With a view to evaluating new anticancer drugs, we are investigating the novel antiestrogen pyrrolidino- 4-iodotamoxifen (idoxifene). [123I]Idoxifene has been prepared in no-carrier-added form using a tributyl stannylated precursor which has been synthesized by means of (2-chloroethoxy)benzene with (±)-2- phenylbutanoic acid on the basis of previously reported standard methods. The biodistribution and dynamic behavior of the compound were investigated using the comparative breast cancer cell line, MCF-7 (estrogen receptor-positive) and MDA-MB-468 (non-estrogen receptor). Results and Conclusion: Acylation of (2-chloroethoxy)benzene with (±)-2-phenylbutanoic acid gave the versatile ketone (81%) which reacted with 1,4-diiodobenzene to give triphenylethylene as a mixture of E and Z geometric isomers, which were separated by the recrystallization in ethanol. The E-isomer was treated with pyrrolidine to give idoxifene (67%). In order to incorporate radioactive iodine into the 4-position, the 4-stannylated precursor was prepared (30%). The yield of radioiodination was 90-92% with a high radiochemical purity greater than 98%. The ratio of tumor uptake of the breast cancer cell line between MCF-7 and MDA-MB-468 was about 1.7.