Single crystals of the LiCoO 2 -LiAlO 2 solid solution compounds LiAl 0.32 Co 0.68 O 2 and LiAl 0.71 Co 0.29 O 2 were synthesized by a flux method using alumina crucibles. A single-crystal X-ray diffraction study confirmed the trigonal R 3m space group and the lattice parameters a ¼ 2.8056(11) A ˚, c ¼ 14.1079(15) A ˚, and c/a ¼ 5.028 for LiAl 0.32 Co 0.68 O 2 , and a ¼ 2.8023(7) A ˚, c ¼ 14.184(4) A ˚, and c/a ¼ 5.061 for LiAl 0.71 Co 0.29 O 2 . The crystal structures have been refined to the conventional values R ¼ 3.2% and wR ¼ 2.4% for LiAl 0.32 Co 0.68 O 2 , and R ¼ 3.6% and wR ¼ 3.5% for LiAl 0.71 Co 0.29 O 2 . The evidence of the location of Al atoms in the pseudotetragonal coordination (6c site), reported previously in LiAl 0.2 Co 0.8 O 2 , could not be observed in the present electron density distribution maps in both LiAl 0.32 Co 0.68 O 2 and LiAl 0.71 Co 0.29 O 2 . The octahedral distortion analysis indicated that the Al-substitution strongly affected the distortion of the LiO 6 octahedron in this solid-solution compound system, but hardly affected that of the (Al.Co)O 6 octahedron.