Cerium- or samarium-modified Cu-SSZ-13 catalysts (Si/Al = 3.6) were prepared through an ion-exchange method. In this way, around 0.3-0.7 wt % Ce or Sm can be introduced into Cu-SSZ-13. Markedly improved structure stability was observed for cerium- or samarium-modified Cu-SSZ-13 containing 2.0-3.3 wt % Cu. The Cu-SSZ-13 sample containing 2.6 wt % copper and its Ce- or Sm-modified counterparts were investigated in detail. According to the characterization of the framework structure (XRD and Al-27 NMR), acidity (NH3-TPD and DRIFTS), and Cu species (EPR and H-2-TPR), we confirmed that the stability of active Cu2+ ions in Cu-SSZ-13 can be enhanced by the coexistence of cerium or samarium ions, which should result in an important contribution to the improvement of the hydrothermal stability of Cu-SSZ-13. In addition, preventing the framework Al from hydrolysis by the exchange of protons with co-cations should be a less important factor.