In₂O₃-sensitized flowerlike ZnO with visible light photoelectric response properties were synthesized by a facile two-step process, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX, HRTEM and UV-vis diffuse reflectance spectroscopy. The results revealed that In₂O₃ nanoparticles have grown and eventually coalesced on the surface of the flowerlike ZnO successfully, and the samples exhibited significant response to visible light. The photoelectric gas-sensing of the In₂O₃-sensitized ZnO was also studied to formaldehyde (HCHO) under 460 nm light irradiation at room temperature with the help of surface photocurrent technique. It was found that ZnO sensitized with In₂O₃ could enhance the gas response to HCHO under the visible light illumination. This may be due to the fact that the composite structure of In₂O₃–ZnO extends the photo absorbing range to visible light area, inhibits the recombination of photo-generated electrons and holes, and thus increases the utilization of photo-generated carriers in photoelectric gas detection, resulting in the higher sensing response in some extent. The gas response to 5 ppm and 100 ppm formaldehyde can reach to 19% and 419% under visible light irradiation at room temperature, respectively. These results should be valuable for designing a new type of visible-light assisted gas sensor at room temperature.