Mitochondrial ADP/ATP carrier (AAC) is a protein catalyzing the transport of adenine nucleotides across inner mitochondrial membrane. In this review article, we first briefly introduce structural and functional properties of this protein. Next, we describe the results of our recent studies on the difference in the C-terminal region between yeast type 2 AAC isoform and bovine type 1 AAC isoform. Furthermore, based on the reactivities of cysteine residues that replaced amino acids in the sixth transmembrane segment, the probable structural features of the C-terminal region of this carrier are discussed.