It shows that calf thymus DNA(CT DNA) can be adsorbed at a highly ordered pyrolytic graphite (HOPG) electrode and detected by differential pulse voltammetry (DPV) and electrochemical atomic force microscopy (ECAFM). It is found that controlled potential pre-polarization influences largely the adsorption of dsDNA while it has little influence on ssDNA. It is demonstrated that ECAFM is useful to exploit adsorption of DNA at HOPGE. The mode of adsorption of DNA at the HOPG electrode that fits best with the experimental data is proposed.