Mechanical method using an attrition-type mill is a useful method to synthesize LiCoO₂ granules consisting of primary nanoparticles without external heating. On the other hand, the heat treatment after synthesis of LiCoO₂ granules is needed to improve its electrochemical performances. Here we report the effect of heating temperature on the battery performances of the LiCoO₂ granule cathode. By heating the LiCoO₂ granules synthesized by mechanical method, the size of primary particles increased with increasing heating temperature from 600℃ to 800℃, whereas the granule structure was maintained. The cathode of LiCoO₂ granules heated at 800℃ exhibited the highest discharge capacity at 0.1 C rate. However, in the case of the charge-discharge tests at high rate, the cathode of LiCoO₂ granules heated at 700℃ showed a high discharge capacity over 70 mA・h/g. The relationship between the microstructure of LiCoO₂ granule and the battery performance was discussed.