In this work, we described gas sensors based on the materials composed of hierarchical flower-like ln₂O₃and reduced graphene oxide (rGO), which were fabricated by a facile one-step hydrothermal method. The rGO-In₂O₃composites exhibited enhanced sensing performance towards NO₂through comparison with the pure In₂O₃sample. The operating temperature can be tuned by the percentage of rGO in the composites. The sensor based on 5 wt% rGO-In₂O₃could work at room temperature with a high response value to 1 ppm NO₂. 3 wt% rGO-In₂O₃composite was adopted for the ultra-sensitivity gas sensor owing to its extremely low limit of detection of 10 ppb with rapid response time to NO₂. The sensor also exhibited excellent selectivity and stability. The ultra-sensitivity of rGO-In₂O₃should be related to synergistic effect of the hierarchical structure of In₂O₃and the presence of rGO in the composites, which provided enhanced surface area and local p-n heterojunctions in rGO/In₂O₃composites.