Abstract: The tables included in the dataset include (1) composition of the olivine host phase determined by electron microprobe analysis. (2) Time of flight Secondary Ion Mass Spectrometric (TOF-SIMS) data and compositions of reaction products of synthetic fluid inclusions after formation of serpentine phases, (3) Reaction rates, H2O fluxes and activities, and error analysis for individual synthetic fluid inclusions with compositions in the H2O-NaCl-MgCl2 system and various starting salinities; (4) Synthetic fluid inclusion microthermometric data, including the ice-melting temperature TM in degrees Celsius, salinity in weight percent calculated from the ice-melting temperature, and amount of water transferred from the solution to hydrous phases calculated based on the change in salinity; (5) Equations and data used to estimate the extent of reaction of each synthetic fluid inclusion analyzed. Other Description: Lamadrid HM, Schwartzenbach E, Dolocan A, Rimstidt JD & Bodnar RJ (2017) Effect of water activity on rates of serpentinization of olivine. Nature Communications, 8, 16107 (in press)