Gas sensing behaviour of cobalt-doped tin oxide (Co–SnO₂) thin films, synthesized by conventional spray pyrolysis technique, has been investigated for carbon dioxide, oxygen and acetone vapour. Structural and elemental analysis of the Co–SnO₂ films was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX). The XRD spectrum revealed the polycrystalline nature of the film with a mixed phase comprising of SnO₂ and Co₃O₄. The surface morphology, as seen in the SEM image, was observed to be granular, uniformly covering the entire substrate surface. The gas/vapour sensing studies performed in dry air at different temperatures in the range of 50–300°C indicated better sensing characteristics for acetone vapour as compared to carbon dioxide and oxygen gases. The influence of cobalt concentration and operating temperature on the sensor performance has also been investigated.