We have proposed a concept “iso-resolution curve” for linear (salt concentration) gradient elution of proteins in electrostatic interaction chromatography (ion-exchange chromatography, IEC). In this study this concept was extended to stepwise elution chromatography. The distribution coefficient was determined from linear gradient elution experiment by using our model. The iso-resolution curves were similar to those for linear gradient elution. However, compared with the curves for linear gradient elution where there was no optimum conditions the curves for stepwise elution showed optimum conditions where the separation can be performed with the shortest separation time and the minimum elution volume consumption.