Uranium and thorium contents of German rock salts were determined by neutron activation analysis. Mean contents of nine samples were 1.07 ppb and 96 ppt for U and Th, respectively. U thus was thought to be depleted and Th was enriched in the solid phase in evaporation of sea water. Similar tendency was observed for other halite samples in nature. These results are consistent with the existence of the stable uranyl tricarbonate anion in the solution phase.