Large-scale In_2O_3 nanotowers with different cross sections were synthesized by a thermal evaporation and oxidation technique using metal as the catalyst. The morphologies and structural characterizations of In_2O_3 nanotowers are dependent on growth processes, such as different metal(Au, Ag or Sn) catalysts, the relative position of the substrate and evaporation source, growth temperature, gas flow rate, and growth time. In_2O_3 nanotowers cannot be observed using Sn as the catalyst, which indicates that metal liquid droplets play an important role in the initial stages of the growth of In_2O_3 nanotowers. The formation of an In_2O_3 nanotower is attributed to the competitive growth model between a lateral growth controlled by vapor–solid mechanism and an axial vapor–liquid–solid growth mechanism mediated by metal liquid nanodroplets. The synthesized In_2O_3 nanostructures with novel tower-shaped morphology may have potential applications in optoelectronic devices and gas sensors. Large-scale In 2 O 3 nanotowers with different cross sections were synthesized by a thermal evaporation and oxidation technique using metal as the catalyst. The morphologies and structural characterizations of In 2 O 3 nanotowers are dependent on growth processes, such as different metal (Au, Ag or Sn) catalysts , the relative position of the substrate and evaporation source, growth temperature, gas flow rate, and growth time. In_2O_3 nanotowers can not be observed using Sn as the catalyst, which indicates that liquid metal droplets play an important role in the initial stages of the growth of In 2 O 3 nanotowers. The formation of an In 2 O 3 nanotower is attributed to the competitive growth model between a lateral growth controlled by vapor-solid mechanism and an axial vapor-liquid-solid growth mechanism mediated by metal liquid nanodroplets. The synthesized In 2 O 3 nanostructures with novel tower -shaped morphology may have potential applications in optoelectronic devices and gas senso rs.