<p>CuO was synthesized using various metal precursors as Cu²⁺ sources via a combined coprecipitation and microwave-assisted hydrothermal method, and its gas-sensing performance was systematically evaluated in relation to its structural, electronic, and morphological properties. This study systematically investigates the role of precursor chemistry as a key parameter in controlling the nucleation and growth of CuO nanostructures under identical synthesis conditions. X-ray diffraction (XRD) confirmed the formation of monoclinic CuO, and the crystallite sizes calculated using the Williamson–Hall method decreased in the order CuO-Chloride &gt; CuO-Nitrate &gt; CuO-Sulfate. Scanning and transmission electron microscopy (SEM and TEM) analyses revealed that all samples were composed mainly of CuO nanorods, with slight differences in thickness and dimensions. The Cu²⁺ oxidation state was further confirmed by X-ray photoelectron spectroscopy (XPS). The three sensors exhibited excellent NO₂ detection at 200&#xa0;°C, with the CuO-N sensor showing the highest response. The limit of detection (LOD) for CuO-N was 0.12 ppm, well below the safety threshold of 1 ppm, demonstrating its capability to detect low NO₂ concentrations. Furthermore, the CuO-N sensor maintained stable responses over four consecutive cycles of 1 ppm NO₂, indicating good operational stability without degradation of its sensing performance. The sensor produced using a metallic nitrate precursor showed the best NO₂ detection response (58% at 200&#xa0;°C) at a low NO₂ concentration (1 ppm). These findings highlight the critical influence of precursor selection on the structural and functional properties of CuO nanostructures and demonstrate a general strategy that can be extended to other metal oxide semiconductors for the rational design of high-performance gas sensors.</p>