Gold species on an oxide support possess variable electronic structures via charge transition so as to increase their chemical redox activity. They are also viably promising for use to enhance gas-sensing response when being exploited in a solid state gas sensor. The synthesis method of the gold-loaded materials plays a crucial role in the functionality. In this paper, we report two types of gold/tin oxide based nanopowders prepared by co-precipitation method and by deposition-precipitation method, respectively. They were evaluated as sensing elements in a semiconductor carbon monoxide (CO) gas sensor. Effects of the material type and CO concentration on sensor response were investigated. Their structural characterizations were done by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. Results demonstrate the surface gold species effective to facilitate CO oxidation in gas atmosphere and promote low-temperature sensor performance.