The adsorption of the oligonucleotides A10, A25, A50 and A80 at the mercury electrolyte solution interface is studied. The oligonucleotides are adsorbed at a potential close to -0.5 V (versus Ag/AgCl reference electrode) but they are desorbed at one or two potential ranges depending on the number of adenine molecules. The effect of the waiting time at the potential of maximum adsorption is studied and this time is closely related to the desorption peak heights. The adsorption/desorption is studied at two oligonucleotide concentrations and at two temperatures. The potentials of the desorption peaks of all oligonucleotides studied have almost the same value, indicating that the desorption process is almost the same. Capacity time curves following potential jumps from the adsorption region to desorption potentials show that the desorption is a very fast process but is usually followed by a reorientation/readsorption of the molecules at the interface depending on the number of adenines.