We studied the binding of [Co(phen)2(HPIP)]Cl3 to mismatched d(GCGAGC)2 containing two sheared G:A mispairs by NMR. The result shows that the complex was intercalated into G:A region from the minor groove and extended to the major groove, and could selectively recognize the mispairs. 31P NMR indicates that the complex binding induced the change of the phosphate backbone in the mismatched base pairs region.