Single phases of M-substituted lithium cobalt oxides, HT-LiCo0.8M0.2O2 (M=Al, Ni), were prepared by molten salt synthesis (MSS) method using coprecipitated Co-M hydroxides in 0.59 LiNO3-0.41 LiOH. The prepared powders consisted of well-developed particles with spherical shape and the particle size was around 150 nm in diameter. Among them, HT-LiCo0.8Al0.2O2 showed an inferior cyclic performance and a smaller discharge capacity than HT-LiCo0.8Ni0.2O2, even though the former is more structurally stable than the latter. Structural analysis of HT-LixCo0.8Al0.2O2 indicated that the Al substitution, causing an enhanced internal resistance for lithium ion diffusion, is responsible for the capacity fading. In the meanwhile, HT-LixCo0.8Ni0.2O2 with large c layer spacing showed as high as 146 mAh/g at the first cycle and 130 mAh/g at the twentieth cycle.