The structural, magnetic, electrical and thermal transport properties of the polycrystalline samples Ca3Co4−xInxO9 (x = 0, 0.05, 0.10, 0.15, and 0.20) have been investigated systematically. The results indicate that the In-substitution has a negative effect on the low-temperature ferrimagnetic transition and the propagation of spin-density-wave. All In-doped samples have a much larger resistivity than that of the un-doped sample. And the temperature region where the Fermi liquid transport mechanism dominates is remarkably widened via In-doping. However, for the In-doped samples, as the In-doped content increases, the value of resistivity ρ decreases monotonously and the electronic correlation in the system enhances. With the addition of In-ions in Ca3Co4O9 system, the thermopower S and the ZT value decrease. The results are suggested to originate from the variations of carrier concentration and lattice disharmony in this system induced by In-doping.