Disclosed are an electrode active material, having a composition of SnPx (0.9≦x≦0.98), an electrode comprising the same, and a lithium secondary battery comprising the electrode. Also disclosed is a method for preparing an electrode active material having a composition of SnPx (0.9≦x≦0.98), the method comprising the steps of: preparing a mixed solution of a Sn precursor, trioctyl phosphine (TOP) and trioctyl phosphine oxide (TOPO); and heating the solution. The application of the teardrop-shaped single-crystal SnPO-94 particles as an anode active material for lithium secondary batteries can provide an anode having very excellent cycling properties because the active material has a reversible capacity, which is about two times as large as that of a carbon anode, along with a very low irreversible capacity, and it is structurally very stable against Li ion intercalation/deintercalation in a charge/discharge process, indicating little or no change in the volume thereof.