<p>ZnO/CNT nanocomposites with different compositions were synthesized and investigated as sensing materials for UV-assisted CO detection at room temperature. XRD, FE-SEM, Raman, and UV–Vis analyses confirmed the formation of ZnO/CNT heterostructures and the interaction between ZnO nanoparticles and CNT networks. The addition of CNT reduced ZnO agglomeration and improved electrical conduction pathways. Ethanol sensing measurements were initially employed to evaluate the effect of composition and identify the optimum ZnO/CNT ratio. The sensing response showed a strong composition dependence, and the Z67–CNT composite exhibited the highest response among the investigated samples. Under UV illumination (365&#xa0;nm), the optimized Z67–CNT sensor exhibited a response of approximately (44.4 ± 2.4) % toward 50 ppm CO at room temperature, together with good repeatability, one-month stability, and enhanced selectivity toward CO over the other tested gases. In contrast, pristine ZnO exhibited a negligible response under the same conditions, indicating that the sensing behavior was strongly influenced by the incorporation of CNTs. The observed p-type resistance response is attributed to the combined effects of UV-assisted oxygen activation on ZnO, interfacial charge transfer between ZnO and CNTs, and charge transport through the CNT percolation network. These effects amplify the resistance modulation associated with CO oxidation reactions at room temperature. The results demonstrate that the CO sensing performance of ZnO/CNT nanocomposites is governed by composition-dependent charge transport and UV-induced interfacial charge modulation, providing an effective strategy for room-temperature CO sensing without external heating.</p>