We have successfully elucidated the microstructures of CexZr1-xO2 solid solutions prepared by co-precipitation and their relation with the reduction behaviors. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy results demonstrate that Zr(IV) occupies initially substituting site and then interstitial site in cubic CeO2. The accumulation of Zr(IV) in interstitial site induces the gradual phase transition from cubic phase to tetragonal phase. The results of selective chemisorption of methyl orange demonstrate that the substituting-site doping of Zr(IV) preferentially occurs in the bulk and then extends to the outmost surface. H-2 temperature-programmed reduction results indicate that the substituting-site doping of Zr(IV) mainly enhances the reducibility of Ce(IV) whereas the interstitial-site doping of Zr(IV) not only enhances the reducibility of Ce(IV) but also lowers the activation energy of reduction reaction. These results provide novel insights into the microstructure-reducibility relation of CexZr1-xO2 solid solutions.