Large-quantity single-crystal SnO2 nanowires coated with quantum-sized ZnO nanocrystals (nc-ZnO/SnO2 nanowires) were directly synthesized by thermal evaporation of SnO powder and a mixture of basic ZnCO3 and graphite powders. A common stainless steel mesh was used to collect the products. The microstructure and possible growth mechanism of the nc-ZnO/SnO2 nanowires were investigated. Results showed that tetragonal structured SnO2 nanowires were obtained, whose surfaces were coated with single-layer ZnO nanocrystals with an average diameter of less than 5 nm. The nanowires had cross-rectangle section with width-to-thickness aspect ratio ranging from 2:1 to 5:1. The lengths of the nanowires were several tens of micrometers. ZnO nanocrystals were single crystalline wurtzite structures, which coated the whole nanowires and distributed uniformly. The possible growth mechanism of the composite nanowires may be enucleated that Zn atoms in the source vapor will replace the Sn atoms on the surface of the formed SnO2 nanowires due to the higher reducibility of Zn than Sri. Two strong Raman scattering peaks at 626 and 656 cm(-1) appeared in the micro-Raman spectrum of nc-ZnO/SnO2 nanowires. The origins of the peaks were discussed. Most importantly, the method can be extended to other composite oxide nanowires that are synthesized by oxidizing two kinds of metals, such as high reducibility elements Mg, Al, Zn, and Ti, and low reducibility elements In, Ge, Ga, etc.