The genetic probe labeled with positron emitter for monitoring tumor cells transfacted by herpes simplex virus thymidine kinase gene has been intensively studied. A useful synthetic methodology was developed to synthesize (E)-5-[2-(tributylstannyl)vinyl]arabinosyl uridine (TSVAU) and to radiolabel (E)-5-{2-[I-125]iodovinyl}arabinosyl uridine (IVAU) substrate for herpes simplex virus type-1 thymidine kinase gene. The synthesis started from arabinosyl uridine via six steps to provide TSVAU in 18% yield. The subsequent radiolabeling with Na[I-125]I under oxidation provided [I-125]IVAU in 80% radiochemical yield.