Thick-film gas sensors were fabricated from nanocrystalline pure and doped Ba0.5Sr0.5MoO4 powders; fine and homogeneously sized powders were prepared using chemical methods such as sol-gel technique. X-ray diffraction (XRD) has confirmed the formation of nanocrystalline Ba0.5Sr0.5MoO4 structure (JCPDS 30–157) for sol-gel powders after annealing. The results obtained from XRD and transmission electron microscope (TEM) show that the powders have nanocrystalline structure and the mean particle sizes of Ba0.5Sr0.5MoO4 powders with and without CuO are approximately 33 and 21.8 nm, respectively. The gas sensing measurements indicate that the Ba0.5Sr0.5MoO4 sensors show good response to H2S and poor response to other reducing gases such as H2, LPG, and CO. The sensitivity was improved by the incorporation of CuO as an additive in Ba0.5Sr0.5MoO4. The maximum sensitivity was obtained for Ba0.5Sr0.5MoO4 with 4 wt% CuO at an operating temperature of 250°C. Also, Pd doping over Ba0.5Sr0.5MoO4 with 4 wt% CuO decreases the operating temperature from 250 to 200°C while increasing the sensitivity to H2S.