A critical evaluation of the mean activity coefficient, &ggr;±, and osmotic coefficient, &fgr;, of aqueous sulfuric acid at 298.15 K is presented for the molality range of 0 to 28 mol⋅kg−1. Osmotic coefficients were calculated from direct vapor pressure measurements, from isopietic measurements or from freezing point depression measurements. Activity coefficients were calculated from electromotive force measurements of galvanic cells. A least‐squares program was used to fit data from all sources using both &fgr; and ln &ggr;±as functions of molality. A nine parameter equation describes the osmotic coefficient, the mean activity coefficient, and the excess. Gibbs energy as a function of the one‐half power of molality. The scientific literature has been covered through January, 1979.