A stable numerical method for the solution of the adsorption integral equation (SAIEUS) is applied to the analysis of potentiometric titration data. A continuous distribution of acidic constants is assumed. The method combines the regularization principle with the B-spline representation of the distribution function. The resolution and reliability of the method are tested on the data obtained for citric acid which is treated as an organic standard. The pK distribution obtained for citric acid consists of three well-separated narrow peaks at pK values corresponding to its pK constants. Integrated areas of the peaks are in excellent agreement with the stoichiometric composition of citric acid. The applicability of the method for characterization of the acidic properties of different materials is further demonstrated using example potentiometric titration data obtained for an ion exchanger, clay minerals, and oxidized activated carbon. The approach presented enables one to assess both qualitatively and quantitatively the number and strength of acidic sites.