NOVELTY - A positive electrode active material contains specific lithium-containing transition metal oxide. The lithium-containing transition metal oxide contains 1 or more of element chosen from VIA group element of periodic table. The crystal distortion and lithium site occupancy rate of the lithium-containing transition metal oxide is 0.15% or less and 99% or more, respectively.    USE - Active material used for positive electrode of non-aqueous electrolyte secondary battery (claimed) used as drive power supply for mobile telephone, notebook personal computer, and smart phone and power supply for electric vehicle and hybrid electric vehicle.    ADVANTAGE - The positive electrode active material provides non-aqueous electrolyte secondary battery with high capacitance and improved durability.    DETAILED DESCRIPTION - A positive electrode active material contains lithium-containing transition metal oxide of formula: Li1+aNixMyO2. The lithium-containing transition metal oxide contains 1 or more of element chosen from VIA group element of periodic table, by an amount of more than 0 and 1 mol% or less with respect to total molar amount of nickel and metal (M). The crystal distortion and lithium site occupancy rate of the lithium-containing transition metal oxide is 0.15% or less and 99% or more, respectively.    M=Co, Mn and/or Al;    a=-0.01 to 0.1;    x=0.7-1;    y=0-0.3;and    x+y=1.    INDEPENDENT CLAIMS are included for the following:    (1) non-aqueous electrolyte secondary battery, which has a positive electrode (11) using the positive electrode active material, negative electrode (12) using the negative electrode active material capable of occluding and discharging lithium, separator arranged between the positive and negative electrodes, and non-aqueous electrolyte (14); and    (2) manufacture of the positive electrode active material, which involves mixing transition metal oxide of formula: NixMyO, lithium carbonate, and the compound containing VIA group element of periodic table, and baking the obtained mixture.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of 3 electrode type test battery.    Three electrode type test battery (10)    Positive electrode (11)    Negative electrode (12)    Reference pole (13)    Non-aqueous electrolyte (14)