Hollow In2O3 spheres were prepared via a P123-assisted one-step solvothermal process for the first time. Ethanol medium played a key role in the direct cubic In2O3 phase formation whereas the triblock copolymer acted as a structure directing agent in the formation of the hollow spheres. The gas sensing properties of the as-prepared In2O3 hollow spheres were investigated. Compared to the products synthesized without P123, the In2O3 hollow spheres exhibited much faster response and higher sensitivity toward HCHO vapor. (C) 2012 Elsevier B.V. All rights reserved.