A lithium-containing composite oxide for a positive electrode for a lithium secondary battery is prepared by formulating a powder mixture by impregnating an N element source powder having an average particle size (D50) ranging from 2 to 20 μm with an aqueous solution of a carboxylic acid having a total of two or more carboxylic acid groups or carboxylic acid groups and hydroxyl groups in its molecule, and optionally, containing an M element, or its salt, and then drying the material obtained; and firing the N element powder material in admixture with a lithium source, optionally, an M element source and a fluorine source, at a temperature ranging from 700° C. to 1050° C. in an oxygen-containing atmosphere, thereby obtaining a lithium-containing composite oxide having the formula LipNxMyOzFa, wherein N is at least one element selected from the group consisting of Co, Mn and Ni, M is at least one element selected from the group consisting of Sn, Zn, Al, alkaline earth metal elements, and transition metal elements other than N, 0.9≦p≦1.1, 0.97≦x≦1.00, 0<y≦0.03, 1.9≦z≦2.1, x+y=1 and 0≦a≦0.02).