In this Article, a high-performance H2S sensor has been successfully prepared using self-assembled polyaniline nano-capsules/zinc oxide hexagonal microdiscs (PANI/ZnO) as a sensitive material. The nanostructure of PANI/ZnO nanocomposite was inspected by a series of characterization methods. The PANI/ZnO nanocomposite sensor demonstrated good selectivity, rapid response/ recovery time, and good reproducibility against H2S gas, which is much better than that of individual PANI and ZnO sensors at room temperature. It is the heterojunction and synergistic effect between the PANI and ZnO that enhanced H2S sensing properties of the PANI/ZnO nanocomposite. This work shows that PANI/ZnO nanoheterostructure is a kind of potential candidate material used to detect H2S gas at room temperature.