Abstract: We experimented with the incorporation of boron into Mg(OH)₂ during its deposition in magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0. The results indicate that the ¹¹B values of the deposited Mg(OH)₂ were higher than those of the associated artificial seawater. The isotopic fractionation characteristics of boron are distinct from those of inorganic carbonate deposition, and indicate that the mechanism for boron incorporation into Mg(OH)₂ also differs from that of inorganic carbonates.