Nearly monodispersed Au38(SC12H25)24 clusters (1.7 ± 0.2 nm) were synthesized using a modified Brust process while utilizing a “thiol etching” approach for the ligand exchange. HRTEM, MALDI, FTIR, and XAS analysis confirmed the formation of the 38-atom clusters in solution. This solution was used to impregnate a microporous TiO2 support to give 0.7% Au38/TiO2 catalyst. Subsequent drying in air and treatment with H2/He at 400 °C removed most of the sulfur ligands, and also increased the Au cluster size to 3.9 ± 0.96 nm. XPS and EXAFS analysis of this supported catalyst showed trace levels of residual sulfides, apparently located at the Au–TiO2 interface. CO oxidation tests on these supported clusters show an activation energy and range of TOFs comparable to those reported by others. These results suggest that supported Au clusters of controllable size can be prepared with this thiol-ligated solution-based method, providing a new approach to the synthesis of these catalysts.