Combinatorial process was applied to the synthesis of layered lithium cobalt manganese oxides using a combinatorial robot system in preparing mixtures of liquid samples and using a combinatorial X-ray diffraction (XRD) apparatus in investigating powders. LiCo1-xMnxO2 (X=0.0, 0.1, 0.2) single phases were synthesized at 1073 K for 5 h in air using LiOH, Co(CH3COO)(2) and Mn(CH3COO)(2) aqueous solutions with molar ratio of Li/(Co + Mn) greater than or equal to 1.3 in mixed solutions. The 16 heated samples in holes of 5-mm diameter and 2-mm depth of a Pt pallet with a size of 35 x 35 x 3 mm were investigated one by one automatically using a combinatorial powder XRD (CrKalpha) apparatus with position-sensitive diffraction counter (PSPC). The device spent 2 min to measure one sample. The results were in good agreement with that obtained by powder XRD (CuKalpha) with a goniometer.