The DNA duplex with tandem T x T mismatches in the presence of Hg(II) has been studied by NMR spectroscopy. For this study, we synthesized decamer duplex with two successive T x T mismatches (TT10). From two-dimensional (2D) 1H-1H NOESY spectrum of TT10 in complex with Hg(II), we were able to trace sequential NOE walks between base protons and anomeric protons (H1'), and assigned all of them. Based on these assignments and NOESY spectra, we could assigned all the non-exchangeable protons of TT10 in the presence of Hg(II).