An adiabatic calorimeter was used to measure the enthalpy of solution of potassium tetrafluoroborate (0.01 mol center dot kg(-1) to 0.02 mol center dot kg(-1)) in water and in aqueous sodium fluoride of different ionic strengths (0.2 mol center dot kg(-1) and 0.5 mol center dot kg(-1)) at 298 K and 313 K. The present results yield the standard-state enthalpy and heat capacity for the solution process and, when combined with literature values for solubilities, yield the standard-state entropy of the solution process. From these properties, and previous measurements involving potassium tetrafluoroborate, we provide a new analysis of thermodynamic properties of the aqueous tetrafluoroborate ion and compare these new properties to previous tabulations and explain the sources of discrepancies in the literature.