In5SnSbO12 is being considered for use in thermoelectric applications. It has a satisfactory electrical conductivity and is expected to possess low thermal conductivity. However, it is difficult to densify In5SnSbO12 by conventional solid-state reaction method. In this work, we demonstrated that Ga doping could increase the relative density of In5SnSbO12, from 60% (x = 0) to 90% (x = 0.1). The improved densification may be attributable to the increased cationic occupancy after the addition of Ga and the reduced grain size induced by the presence of the secondary phase Ga2In6Sn2O16. The improved relative density led to a significant reduction in electrical resistivity; for example, for x = 0.1, the lowest electrical resistivity was 0.002 Omega cm at 973 K, which was five times lower than that of the undoped sample (x = 0). The resultant power factor of this sample had a value of 3.4 x 10(-4) Wm(-1) K-2 at 973 K, which was nearly four times higher than that of the undoped sample. Although thermal conductivities were increased with Ga doping due to the enhanced densification, they were lower than that of In2O3. The highest thermoelectric performance was achieved in the sample with x = 0.05, specifically zT 0.17 at 973 K. These results indicate that the addition of Ga to In5SnSbO12 results in a material which is more promising for thermoelectric applications.