Cobalt-doped todorokites were synthesized by refluxing process at atmospheric pressure from the transformation of birnessites. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), scanning electron microscope (SEM) and chemical composition analysis were used to characterize the crystal structures, surface morphologies and chemical compositions of synthesized products. Results showed that all refluxing products were todorokites with 3×3 tunnel structure and the chemical compositions were denoted as Mg x Co y MnO z ·nH2O, where 0.18≤ x ≤0.22, 0≤ y ≤0.31, 2.01≤ z ≤2.52 and 0.35≤ n ≤ 0.73. Cobalt-doped todorokites were investigated as cathode materials of lithium rechargeable batteries for charge/discharge characteristics. Discharge capacity of the undoped todorokite was about 211mAhg−1 at first cycle, and then decreased to 37mAhg−1 after 30 cycles. The cyclic capacities of todorokite could be improved remarkably by substitution of cobalt for manganese. Todorokites with Co content of 10–15% displayed better discharge performance. Mg0.18Co0.12MnO2.19·0.45H2O with Co content about 10% showed a high initial discharge capacity of 219mAhg−1 and cycling capacity of 102mAhg−1 after 100 cycles. The effect of doping cobalt on electrochemical performance of todorokite was further proved with cyclic voltammetry by using powder microelectrode.