Owing to the requirement for high-performing and low-cost gas sensors, Ag:Y2O3-SnO2 core-shell nanocomposites were fabricated for high-efficiency gas sensing applications. Thick film sensor of Ag:Y2O3-SnO2 was prepared through a simple slurry coating method and tested towards various volatile organic compounds (VOCs). Ag:Y2O3-SnO2 sensor has exhibited superior sensing performance and good stability at room temperature when introduced to low concentrations (1 ppm) of ammonia. Ag:Y2O3-SnO2 sensor has shown a rapid response time (2 s) and recovery time (8 s) as well as increased sensitivity (similar to 1496) towards 100 ppm of ammonia at room temperature. HR-TEM results show the core-shell structure of Ag:Y2O3-SnO2 with sizes around 6-18 nm. The sensing performance of the Ag: Ag:Y2O3-SnO2 sensor is shown extensively high compared to the pure Y2O3, SnO2 and Ag:Y2O3-SnO2 sensors.