NOVELTY - Nonaqueous secondary battery comprises: positive electrode (1) having positive electrode mixture layer, negative electrode (2) and nonaqueous electrolyte, where the positive electrode contains, as an active material, at least two lithium-containing transition metal oxides having different average particle sizes. The lithium-containing transition metal oxide having smallest average particle size is lithium-containing transition metal oxide (I), the positive electrode mixture layer has density of at least 3.5 g/cm3 and nonaqueous electrode mixture contains a compound having two nitrile groups.    USE - The nonaqueous secondary battery is used as a power source of e.g. notebook personal computer, notebook word processor, electronic book player, cellular phone, codeless handset, pager, portable terminal, portable copier, electrical notebook, electronic calculator, liquid crystal TV set, electric shaver, electric power tool, tape recorder, radio, headphone stereo, handy printer, portable CD player, navigation system, refrigerator, air conditioner, water heater, microwave oven, dishwasher, washing machine, drying machine, automobile, electric vehicle and golf cart.    ADVANTAGE - The nonaqueous secondary battery exhibits high capacity, good charge-discharge cycle characteristics and high reliability such as safety. In the battery, the reaction of the positive electrode and the nonaqueous electrolyte is suppressed, thus the expansion of the battery during the storage of the charged battery at high temperature prevented, and the storage characteristics of the battery is improved.    DETAILED DESCRIPTION - Nonaqueous secondary battery comprises: a positive electrode (1) having a positive electrode mixture layer, a negative electrode (2) and a nonaqueous electrolyte, where the positive electrode contains, as an active material, at least two lithium-containing transition metal oxides having different average particle sizes. The lithium-containing transition metal oxide having the smallest average particle size is a lithium-containing transition metal oxide of formula (I), the positive electrode mixture layer has a density of at least 3.5 g/cm3 and a nonaqueous electrode mixture contains a compound having at least two nitrile groups in the molecule.    M1 = at least one transition metal element comprising Co, Ni or Mn;    M2 = Mg and/or at least one metal element comprising Ti, Zr, Ge, Nb, Al or Sn;    M3 = an element other than Li, M1 and M2;    x = 0.97 to less than 1.02;    y = 0.8 to less than 1.02;    z = 0.002-0.05; and    v = 0-0.05, where a content of Mg in (I) is 0.15 mole% to less than 2 mole% based on an amount of the metal element M1.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the nonaqueous secondary battery.    Positive electrode (1)    Negative electrode (2)    Battery case (4)    Insulator (5)    Electrode laminate (6)