A pre-concentration method for rare-earth elements in environmental water samples using chelating resin disk was developed. All rare-earth elements plus Th and U in environmental water samples were determined by ICP-MS. The preconcentration of all rare-earth elements, (Th and U) and the removal of major elements in seawater, such as alkali and alkaline- earth elements, could be carried out quickly by adjusting the sample's pH to 3. By this method barium could be removed along With other alkaline-earth elements from the sample. This reduced the interference of BaO when using ICP-MS, which allowed the analysis of europium with good precision. Using this method, rare-earth elements in four environmental standard samples (river water standard sample, JAC0031 (Japan Society for Analytical Chemistry), SLRS-3 (NRC Canada), seawater standard sample CASS-3, NASS-4 (NRC Canada)) and five environmental samples in Aomori (seawater 1, sea mingled with brackish water 3, fresh water 1) were measured.