We studied the magnetic and thermoelectric properties of the homologous series An+2CoBnO3n+3 (A=Ca,Sr, B=Co,Rh,Ir; n=1–3), which possess one-dimensional chain structures consisting of one CoO6 trigonal prism and n BO6 octahedra. Both Ca3CoRhO6 and Ca3CoIrO6, the n=1 members, exhibited an abrupt drop in the magnetic susceptibility (χ) at around 35 K with decreasing temperature. A broad peak was observed in the χ-T curves at 13 and 5 K, respectively, for the n=2 and 3 samples of the B=Rh series. The change in the magnetic behavior of the B=Rh samples with increasing n is attributable to the increase of interchain distance, while the difference of Ca3CoRhO6 and Ca3CoIrO6, despite the valence and spin state are the same, may be due to a structural distortion of the latter compound. Thermopower (S) of all three n=1 samples was about 150 μV/K at around 1000 K, and resistivity (ρ) showed semiconductive behavior, with Ca3CoRhO6 having the lowest resistivity. As a result, the power factor (=S2/ρ) of Ca3CoRhO6 at 1073 K was more than two times larger than that of Ca3Co2O6.