Ga- and In-modified ceria (Ce0.8Ga0.2O2, Ce0.8In0.2O2) materials were used as supports for cobalt-catalyzed Fischer-Tropsch synthesis (FTS). The addition of Ga to ceria was found to improve CO conversion for cobalt-catalyzed FTS, while the addition of In tended to decrease it. A similar trend was observed with the Ag-promoted cobalt/ceria catalysts. Doping of ceria with Ga or In decreased methane and increased the selectivity to olefins and alcohols for Ag-promoted cobalt/ceria. The sum of the products of olefins and alcohols for various catalysts exhibited a decreasing trend as follows: Ag-Co/Ce-Ga > Ag-Co/Ce-In > Ag-Co/Ce. Results of H-2-TPR-XANES showed that adding of Ga or In to ceria increases the fraction of Ce3+ in the surface shell for both unpromoted and Ag-promoted catalysts in the range of temperature typical of catalyst activation. This partially reduced ceria plays an important role in controlling the product selectivity of cobalt-catalyzed FT synthesis.