The self-diffusion of H218O has been studied empirically in Dead Sea brine (TDS≈340 g/l), a natural, very saline solution composed of mainly Mg and Na chlorides. Experiments were conducted in dialysis cells with 18O-depleted water at an ambient temperature of 22¿1 ¿C. The self-diffusion coefficient in DS water is 1.8¿10-5 cm2/sec, about 25% lower than the known self-diffusion coefficient in distilled water. Knowledge of the self-diffusion coefficient in hypersaline solutions is of importance for the determination of mass transfer in brines, at sediment-water interfaces in lakes and in interstitial solutions of saturated and unsaturated porous media in aquifers. ¿ American Geophysical Union 1996