Abstract It is well known that boric acid exhibits various toxic effects on plant, animal and human beings even at very low concentrations. Thus, the development of boron-removal technique from wastewater has been intensively investigated. In this study, a new hydrothermal treatment technique was developed to recover boron as recyclable precipitate Ca 2B 2O 5·H 2O from aqueous solutions. As a result, it was found that the hydrothermal treatment using calcium hydroxide as a mineralizer converted boron in the aqueous media effectively into calcium borate, Ca 2B 2O 5·H 2O. In the optimal hydrothermal condition, more than 99% of boron was collected from the synthetic wastewater of 500 ppm. Thus, the present hydrothermal treatment in the presence of calcium hydroxide is recommended as one of the effective techniques to recover boron from aqueous media.