This dataset provides 87Sr/86Sr in hydrothermal precipitates recovered at the Brothers volcano. Samples originate from the NW Caldera and the Upper Caldera vent sites and were retrieved during RV Sonne cruise SO253 in December 2016/January 2017 and during RV Thompson cruise TN350 in March 2018. All samples were analyzed using Thermal Ionization Mass Spectrometry (TIMS). The dataset contains measurements of 87Sr/86Sr in single crystals of anhydrite or barite and measurements of 87Sr/86Sr in sulfate bulk samples composing of anhydrite and/or barite.