We have successfully fabricated two different types of grain-aligned bulks of thermoelectric Bismuth-based cobalt oxides using a magnetic grain-alignment process. The Pb-doping in (Bi2Sr2O4) 0.55CoO2, which shows an easy axis of magnetization parallel to the a-axis, was effective for enhancement of magnetic anisotropy along the a-axis, while the Ca-doping in [(Bi0.5Pb 0.5)2Sr2O4]0.55CoO 2 converted the easy axis along the a-axis to that along the c-axis. Moreover, the magnetic anisotropy along the c-axis was enhanced by the partial Pr-doping for the Ca sites. The changes of their crystal structures revealed that distortion of the block layer was arisen from the substitution of the Ca-doping or the co-doping of Ca and Pr for the Sr sites in [(Bi 0.5Pb0.5)2Sr2O4] 0.55CoO2, leading to the changes of their magnetic anisotropies through locally structural distortion of the CoO2 layers. The c-axis and a-axis grain-aligned bulks were fabricated by the slip-casting method under a magnetic field of 10 T for [(Bi0.5Pb 0.5)2(Ca0.8Pr0.2)2O 4]pCoO2 and [(Bi0.75Pb 0.25)2Sr2O4]0.55CoO 2, respectively. Especially for the c-axis grain-aligned bulk, microstructure observation showed highly grain-oriented, and large reduction of resistivity was observed in a perpendicular direction to the applied field. The control of the easy axis of magnetization by a crystallochemical process is useful for the application of a magnetic grain-alignment process.