H2S is a gas that can be hazardous to human health, even at low concentrations. Several studies have shown that people living near paper mills and oil and gas factories experience health problems and suffer from allergic reaction symptoms, including eye, nose, and respiratory symptoms in children and adults triggered by exposure to H2S gas with concentrations of less than 100 ppb. In this study, we used biomass activated carbon produced from rubber fruit shells as a decoration material prepared with a chemical activating agent (KOH) with an impregnation ratio of 1:5. The process produces biomass activated charcoal with a carbon content of 79.05%. Then, 5% of the weight of the rubber fruit shell carbon was mixed with ZnO by a wet chemical process as a sensor material placed on a Au electrode. The sensing response was tested at H2S concentrations of 20, 30, 40, 50, 60, 70, 80, 90, and 100 ppb at room temperature (25 ℃). The results of the sensing response were 2.95, 4.60, 5.62, 5.94, 6.47, 6.62, 7.41, 8.84, and 10.00%, respectively. The research results showed that the ZnO gas sensor decorated with carbon can detect H2S gas of less than 100 ppb. Additionally, this sensor can be operated at room temperature.