A critical evaluation of the mean activity γ±, and osmotic coefficients, φ, of aqueous alkali metal nitrites at 298.15 K is presented for the molality range from dilute to saturation. Osmotic coefficients were calculated from static vapor pressure measurements. A nonlinear least-squares program was used to fit φ data as a function of molality. Several equations describe the osmotic coefficient, the mean activity coefficient, and the excess Gibbs energy as a function of the square-root of molality for each slit. The scientific literature was covered through March 1979.