The structure and dynamics of alkali cations at the water/liquid mercury interface are studied by molecular dynamics. The simulations indicate the adsorption of all;ali cations at the interface. The adsorption of the ions changes the structure of the mercury atoms in the first layer. The structure of the rest of the hydration sphere is similar to the bulk one in many features because the metal surface is mostly affected by its excluded volume. The dynamics of the ions are determined by the cages formed by the water molecules strongly bound to the mercury atoms at the interface.