ZnO nanostructures of rod-like morphology were synthesized through a low-temperature hydrothermal process. Incorporation of indium in the nanostructures during synthesis was not successful due to the formation of In(OH) 3 phase. A post-deposition thermal annealing process in inert atmosphere resulted effective for the dissociation of In(OH) 3 phase and doping of indium into the nanostructures. Effect of indium doping on the structure, morphology and optical absorption of the nanostructures are studied. Beyond a certain concentration, the incorporated indium form phase separated oxide instead of being doped. Incorporated indium occupy the zinc sites in the nanostructures.