Electrochemical impedance spectroscopy (EIS) has been applied to measure the HS gas response of the sensor fabricated on reduced graphene oxide (rGO)-incorporated nano-zinc oxide (n-ZnO) composites. These nanocomposites were prepared by a facile one-step solution route at room temperature. The structural, surface morphological, and elemental analyses of the composite material have been investigated. EIS was carried out to study the HS gas-sensing properties of fabricated sensors. The developed sensor showed an optimal HS gas response to various concentrations ranging from 2 to 100 ppm at 90 °C. The HS gas-sensing performances of pure n-ZnO and various concentrations of rGO-incorporated n-ZnO were evaluated. The HS gas-sensing results showed that n-ZnO/rGO composites exhibited high response when compared to pure n-ZnO. The enhanced HS response was speculated to be ascribed due to two factors. First, rGO creates reactive sites for HS molecule adsorption. Second, rGO has great electrical conductivity compared to n-ZnO that enables the active transport of electrons from HS gas on interaction with the sensing layer, resulting in enhanced gas response at 90 °C temperatures.