The solubility of K2Cr2O7 in water at 25 degrees C was determined by using the evaporating method in the presence of various concentrations (0, 0.0500, 0.100, ..., 1.800 mol.L-1) of NaNO3. The values of solubility and solubility product constant was evaluated at zero ionic strength upon the extrapolation method. Using the value of solubility product constant obtained by the extrapolation method enables us to calculate the extension of ion-pairing in the saturated solution of K2Cr2O7 at 25 degrees C. On the other hand, the ion-association phenomenon could be explained by the Bjerrum theory or contact ion-pair model of Fuoss theory.