Geothermal water from geothermal plants often contains high levels of boron (B), above the Japanese effluent standard level. To establish an effective utilization system for geothermal resources, boron removal using non-calcined and calcined hydrotalcite was investigated using geothermal water from the Sumikawa geothermal plant in Japan. Calcined hydrotalcite removed large amounts of boron, and changed the solution pH to 12, while non-calcined hydrotalcite removed little boron. Calcined hydrotalcite are also more effectively removed from other anions including Si, As, F−, Cl−, and . The concentrations of boron dropped to below the Japanese effluent standard level of 10 mg L−1 with a 6 h treatment with calcined hydrotalcite. The ability of calcined hydrotalcite to remove boron from geothermal water was almost constant over the temperature range 25–80°C.