Ce(l-x)La(x)O(2-delta) (0 < or = x < or = 0.2) nanoparticles have been synthesized by a sol-gel method and a hydrothermal method, respectively. Nanoparticles have been obtained and the optimum synthesis parameters and microstructural characteristics have also been studied. High purity and well-dispersed nanoparticles with a narrow grain size distribution of 10-20 nm have been obtained. Sol-gel method was much more superior than the hydrothermal method in synthesizing particles in small average crystal size. The microstructure characteristics showed that there were (111) and (200) planes with the angle of 53.9 +/- 0.8 degrees for Ce0.8La0.2O1 9 and (100) and (101) planes with the angle of 30.85+/-0.75 degrees for La2O3 in the lattice, respectively. The formation mechanism of the solid solution has been discussed and the maximum percentage of La2O3 in Ce(l-x)La(x)O(2-delta) (0 < or = x < or = 0.2) solid solution was near to 20 percent.