To provide a process for producing a surface modified lithium-containing composite oxide, which is excellent in discharge capacity, volume capacity density, safety, durability for charge and discharge cycles and an excellent rate property, at a low production cost.The present invention is characterized in that a process for producing a surface modified lithium-containing composite oxide, wherein a lithium titanium composite oxide is contained in the surface layer of particles of a lithium-containing composite oxide represented by the formula: LipNxMyOzFa, where 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 Al, Sn, alkaline earth metal elements and transition metal elements other than Co, Mn and Ni, 0.9≦p≦1.3, 0.9≦x≦2.0, 0≦y≦0.1, 1.9≦z≦4.2, and 0≦a≦0.05, which comprises impregnating a solution having a lithium source and a titanium source dissolved therein, followed by heat treatment at a determined temperature, to obtain the surface modified lithium-containing composite oxide, wherein the titanium contained in the surface layer is from 0.01 to 1.95 mol %.