This work is devoted to the structural and morphological study of co-doped Y2O3:Yb3+-Er3+ nanophosphors, with 1 mol% of Er2O3 and 2 mol% of Yb2O3, synthesized by hydrothermal precipitation method via cetyltrimethylammonium bromide (CTAB) surfactant complex for different ethanol/water solvent ratios ranging from 1:1 to 1:10. Structural characterization results showed the prevalence of cubic phase independent of the solvent ratio although particle size does depend on the solvent ratio. Concerning to morphology, microscopic characterization indicates that the content of water used in synthesis is determinant in the morphology of resulting samples: a high content of water favored the formation of nanorods/nanofibers while a low water content give rise to heterogeneous morphology with irregular particles. Also, solvent ratio determines the consistency of nanostructured materials; an intermediate solvent ratio leads to nanofibers while a high solvent ratio let to obtain nanorods with length/diameter ratio ~3-5. These results show that solvent concentration plays an important role in particle size and morphology of nanostructured materials while the annealing temperature determines the phase composition and crystallite size.