The lithium intercalation property of cobalt vanadium oxide CoV3O8 having tunnel space along the c-axis of the crystal structure was investigated. Lithiated samples, LixCoV3O8, were structurally analyzed by the Rietveld analysis. From the linear variation in the lattice parameters during lithiation, it was found that lithium was intercalated in the host compound CoV3O8 for 0.125 < x < 0.5 in LixCoV3O8. For x>0.5, no change in the lattice parameters was observed and an amorphous substance was formed. The variation in the interatomic distances between oxide ions indicated that O(5) was at the apex of LiOx polyhedra. On the basis of the cavity size and molar ratio Li/CoV3O8, the 16k (similar to 0.01,similar to 0.07,similar to 0.11) site in the tunnel space was found to be suitable for lithium intercalation.