Zirconium-doped Li 1.1 Co 1?x Zr x O₂ (0≤x≤0.05) powders as cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis method. Cyclic voltammetry and cyclic stability tests were performed, and the changes of microstructure were observed. The solubility limit of zirconium into Li 1.1 CoO₂ was less than 5 mol%, and monoclinic Li₂ZrO₃ phase was formed above the limit. The Zr-doping suppressed the grain growth and increased the lattice parameters of the hexagonal LiCoO₂ phase. The Zr-dopiong of 1 mol% resulted in the best cyclic performance in the range of 3.0~4.3 V at 1C rate (140 ㎃/g); the initial discharge capacity decreased from 158 ㎃h/g to 60 ㎃h/g in the undoped powder, while from 154 ㎃h/g to 135 ㎃h/g in the Zr-doped powder of 1 mol% after 30 cycles. The excellent cycle stability of Zr-doped powder was due to the low polarization during charge-discharge processes which resulted from the delayed collapse of the crystal structure of the active materials with Zr-doping.