NOVELTY - Active material comprises a composite oxide comprising e.g. lithium, niobium, tantalum, titanium, and oxygen.    USE - The active material is useful for preparing non-aqueous electrolyte battery and battery pack (all claimed). The non-aqueous electrolyte battery is used as a power source for hybrid vehicles, electric cars, and uninterruptible power supply for base stations and for portable telephone.    ADVANTAGE - The crystal structure of the monoclinic composite oxide has a large space into which lithium ions can be equivalently absorbed, and has a structural stability. Moreover, the monoclinic composite oxide can be more improved in an energy density than a compound containing no pentavalent cation. Further, the monoclinic composite oxide can improve the absorption properties of the lithium ions to the absorption space and the release properties of the lithium ions from the absorption space, and can effectively increase a space contributing to the absorption and release of the lithium ions. The monoclinic composite oxide can provide a high capacity. The non-aqueous electrolyte battery using the composite oxide capable of having a crystal lattice having a larger volume as the active material can have further improved repeated charge-and-discharge performance. As a result, the non-aqueous electrolyte battery can exhibit more excellent life characteristics. Since the non-aqueous electrolyte battery having a charge and discharge curve having a higher gradient easily associates a potential change with a battery capacity during charge and discharge, the remaining capacity of the battery can be more easily managed.    DETAILED DESCRIPTION - Active material comprises a composite oxide represented by Lix(Nb1-yTay)2+0.5zTi1-zM0.5zO7.    x=0-5;    y and z=0-1; and    M=metal element selected from Sc, Y, V, Cr, Fe, Co, Mn, Al, and Ga.    INDEPENDENT CLAIMS are included for:    (1) a non-aqueous electrolyte battery comprising a negative electrode containing the active material; a positive electrode; and a non-aqueous electrolyte; and    (2) a battery pack comprising non-aqueous electrolyte battery, where the non-aqueous electrolyte battery comprises a negative electrode containing the active material a positive electrode, and a non-aqueous electrolyte.