Disclosed is a method of preparing a cathode active material useful in a sodium ion secondary battery having high reversible capacity and excellent cycle characteristics. The method for preparing a cathode active material composed of Zrw-doped NaxLiyMzOa includes the steps of (A) doping LiyMzOa with Zrw to provide Zrw-doped LiyMzOa; and (B) dissociating Li ion from the Zrw-doped LiyMzOa and inserting Na ion thereto to provide the Zrw-doped NaxLiyMzOa, wherein M is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo, Ru, and combinations thereof, and wherein 0.005