We report here for the first time the hollow, metastable, single-crystal, rhombohedral In2O3 (rh-In2O3) nanocrystals synthesized by annealing solvothermally prepared InOOH solid nanocrystals under ambient pressure at 400 degrees C, through a mechanism of the Kirkendall effect, in which pore formation is attributed to the difference in diffusion rates of anions (OH and O-2) in a diffusion couple. The InOOH solid nanocrystals were prepared via a controlled hydrolysis solvothermal route by using In(NO3)(3)center dot 4.5H(2)O as a starting material and glycerol-ethanol as a mixed solvent. The glycerol-ethanol mixed solvent plays a key role on the formation of the intermediate InOOH, thus the final product of rh-In2O3. The as-synthesized In2O3 nanocrystals present excellent photocatalytic degradation of rhodamine B (RhB) and methylene blue (MB) dyes, which present similar to 92% degradation of RhB or MB after 4 or 3 h reaction in the presence of the as-synthesized In2O3 nanocrystals, respectively.