Lithiation characteristics of a complex oxide containing V(V) and Cu(II), Cu5V2O10, were investigated. Lithiation was carried out chemically using an n-BuLi/hexane solution. The valence stales of copper and vanadium and the structural changes upon lithiation were analyzed using esr, XRD and ir measurements. It was revealed that reduction processes occurred consecutively with an increasing extent of lithiation, x = Li/(5 Cu + 2 V). Up to x = 3, preferential reduction of Cu(II) to Cu(I) occurred in the single phase. At 3 < x, Cu(II) was reduced to Cu(O) and Cu(II) (LiCuVO4) in the multiphase system. Above about x = 6, LiCuVO4 was further reduced to metallic copper. The open-circuit potentials of lithiated Cu5V2O10 decreased with x gradually at 0 < x < 3, and has a plateau at x > 3.