Metal oxide semiconductors (MOS)-reduced graphene oxide (rGO) nanocomposites have attracted great attention for room-temperature gas sensing applications. The development of novel sensing materials is the key issue for the effective detection of ammoniagas at room temperature. In the present work, the novel reduced graphene oxide (rGO)-In2O3 nanocubes hybrid materials have been prepared via a simple electrostatic self-assembly strategy. Characterization results exhibit that the intimate interfacial contact between In2O3 nanocubes and the rGO sheets are achieved. Particularly, the as-prepared rGO/In2O3 nanocomposites displayed high sensitivity, fast response and excellent selectivity towards ammonia (NH3) at room-temperature, which clearly uncovers the merit of structural design and rational integration with rGO sheets. The superior gas sensing performance of the rGO/In2O3 nanocomposites can be attributed to the synergetic effects of rGO sheets and porous In2O3 nanocubes. The reported synthesis offers a general approach to rGO/MOS-based semiconductor composites for room-temperature gas sensing applications.