The complete nucleotide sequence of rat Uncoupling Protein gene has been determined. 4.5 Kb of the 5′-flanking region have also been sequenced. The site of transcription start as well as 3′-end extremities were identified. Transcription unit spans 8.4 Kb and contains 6 exons and 5 introns. Uncoupling protein as well as related mitochondrial carriers such as ADP/ATP carrier and phosphate carrier has a triplicated structure and each repeat of Uncoupling Protein corresponds to 2 exons. Two gene duplications could explain the triplicated structure of UCP and the more recent event of duplication concerned exons III and V. Evidence for homology between Uncoupling Protein and Neurospora crassa ADP/ATP carrier at the gene level was also noticed.