The kinetic and thermodynamic studies of the insertion of lithium into hexagonal‐type ( , ), obtained by heat‐treating the corresponding tungstic acid C phases, , at 350°C in air, were made. The variations of quasi‐open‐circuit potentials and x‐ray diffraction patterns of the tungsten oxides with lithium insertion revealed that a ternary phase, such as , is formed, while maintaining the original hexagonal‐type structure. The standard free energies for lithium insertion, , were −375, −389 and −400 kJ(mol)−1 at 298 K for , respectively. The chemical diffusion coefficients of lithium, , in the oxides were measured as functions of the lithium composition and temperature by an ac impedance method using carbonate as an electrolyte. The obtained values of , based on a geometrical surface area, were dependent on the lithium composition and temperature. The values of for were approximately 10−8 cm2 s−1 at and room temperature, decreasing to 10−10 cm2 s−1 with increasing . The self‐diffusion coefficient of lithium, , derived from the values, was of the order of 10−11 cm2s−1 at and room temperature, decreasing with increasing . Both the values of and for the hexagonal‐type oxides were by several orders of magnitude higher than those for the monoclinic . The activation energies for lithium diffusion in were , being typical of diffusion in layered insertion materials.