The catalytic behavior of CeO 2 -based solid solution catalysts (Ce 0.7 Zr 0.3 O 2 , Ce 0.7 Pr 0.3 O 2−δ , and Ce 0.7 Gd 0.3 O 1.85 ) had been studied for soot combustion. These catalysts were characterized using X-ray diffraction (XRD), UV-visible, Raman, and H 2 temperature-programmed reduction (H 2 -TPR) measurements. The Zr, Pr, and Gd cations replaced Ce cations in the CeO 2 lattice to form nanocrystalline CeO 2 -based solid solutions. The crystallite size of Ce 0.7 Zr 0.3 O 2 , Ce 0.7 Pr 0.3 O 2−δ , and Ce 0.7 Gd 0.3 O 1.85 is 7.3, 7.8, and 11.1nm, respectively, which are much smaller than pure CeO 2 (36.2nm). The substituting process can promote the formation of oxygen vacancies, which can hasten the diffusion rate of oxygen, then improve the combustion activity. According to the catalytic soot combustion results, the ranking in activity of these catalysts is Ce 0.7 Zr 0.3 O 2 >Ce 0.7 Pr 0.3 O 2−δ >Ce 0.7 Gd 0.3 O 1.85 ∼CeO 2 , which is well consistent with the reducibility sequence of the samples. The mass of catalyst plus soot mixture have effect on soot combustion: the T ig and T max decrease with the increasing of sample weight. Combustion activity of catalysts decreases slowly with cycled runs, which can be attributed to the activity lost of catalyst.