In2O3 nanofibers and nanoribbons were prepared by electrospinning combined with a poly(vinyl pyrrolidone)-assisted sol gel technique. By tuning the experimental parameters, the morphological transformation of In2O3 from nanofibers to nanoribbons was achieved. It was found that both the rapid evaporation of solvent and the concentration of the precursor played important roles in the formation process of In2O3 nanoribbons. The average diameter of the In2O3 nanofibers is 180 nm. The nanoribbons have an average width of 1 mu m and a thickness of about 150 nm. The lengths of both can reach millimeters. The average grain size consisting of nanofibers and nanoribbons is 18.6 and 11.2 nm, respectively. The gas-sensing properties of In2O3 nanofibers and nanoribbons toward formaldehyde vapor were investigated. Interestingly, the gas sensor fabricated with In2O3 nanoribbons exhibited a higher and faster response at a relatively lower operating temperature than that fabricated with nanofibers.