Using the spark plasma sintering process In2-xCexO3 (0 = x = 0.10) fine grained ceramics have been synthesized. Our results indicate that all the In2O3-based ceramic samples show good electrical conductivity and high thermoelectric power factor. In comparison with pure In2O3 bulks or doped samples with grain size above 1 mu m, the 100300 nm fine grain In2O3-based ceramics exhibit much lower thermal conductivities (1.92.5 W center dot(m center dot K)-1 at 1173 K), demonstrating a remarkable cooperative tuning effect imposed by grain size reduction and nano-clusters formation. The maximum figure of merit ZT value is optimized up to 0.47 at 1223 K for In1.92Ce0.08O3 sample, which makes them promising candidates for thermoelectric applications.