Two indacenodithiophene (IDT)-based conjugated polymers, PIDT-EDOT and PIDTT-EDOT, were designed and synthesized as organic thermoelectric materials. Compared to PIDT-EDOT, the IDT unit of PIDTT-EDOT was extended by incorporating two thieno[3,2-b]thiophene (TT) units into the polymer main chain. The polymer PIDTT-EDOT showed better thermal stability and more planar conjugated structure than PIDT-EDOT. Meanwhile, different thermoelectric properties were observed when the two polymer films were doped with FeCl3. PIDTT-EDOT showed better thermoelectric properties than PIDT-EDOT, and the highest power factor observed for PIDTT-EDOT was 0.867 mu W m(-1) K-2 at 453 K, which is approximately 25 times higher than that of PIDT-EDOT. These results indicate that a slight change in the polymer main chain will have a great impact on the thermoelectric properties of IDT-based conjugated polymers. The data presented herein can be used as a reference for the design of new high-performance thermoelectric materials.